Apparatus and method of video playback

ABSTRACT

A method of video playback includes obtaining a 3D reconstruction of at least part of an environment, obtaining video footage of an activity within that at least part of the environment, obtaining data indicating a position and orientation of a first camera within the at least part of the environment that recorded the obtained video footage, and rendering a view of the video footage in alignment with a corresponding view of at least part of the 3D reconstruction, responsive to the position and orientation of the first camera within the at least part of the environment.

BACKGROUND

The present invention relates to and apparatus and method of mapping avirtual environment.

Players of videogames often want assistance, either to progress within agame if they are stuck or want to discover additional features, or ifthey want to see examples of good play to improve their own performance,for example to beat a personal best score.

Video captures of in-game footage, optionally together with commentaryby the creator of the video (for example walk-throughs and speed-runs onYouTube®, or e-sports on Twitch®) are popular as guides orentertainment, but what they show is limited by the choices made by thecreator of the video.

As a result, the benefit of such videos to a viewer wanting assistancefor a videogame or to be entertained by it can be highly variable.

SUMMARY

The present invention seeks to address or mitigate this issue.

Further respective aspects and features of the invention are defined inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an entertainment device operable as oneor more of the video recording apparatus, video playback apparatus andevent analyser in accordance with embodiments of the present invention.

FIG. 2 is a schematic diagram of a system comprising a video recordingapparatus, video playback apparatus and event analyser in accordancewith embodiments of the present invention.

FIG. 3 is a flow diagram of a video recording method in accordance withembodiments of the present invention.

FIGS. 4A and 4B illustrate a video image and corresponding depth bufferinformation in accordance with embodiments of the present invention.

FIG. 5 is a flow diagram of a video playback method in accordance withembodiments of the present invention.

FIG. 6 illustrates an augmentation of a video with a graphicalrepresentation of a statistically significant in-game event, inaccordance with embodiments of the present invention.

FIG. 7 is a flow diagram of an event analysis method in accordance withembodiments of the present invention.

FIGS. 8 to 11 are example illustrations of possible augmentations of avideo recording of gaming footage, in accordance with embodiments of thepresent invention.

FIG. 12 is a flow diagram of a method of mapping a virtual environmentin accordance with embodiments of the present invention.

FIGS. 13A and B illustrate the process of obtaining depth informationfor a predetermined set of points in a video image, in accordance withembodiments of the present invention.

FIG. 13C illustrates mapping points in a map space in accordance withembodiments of the present invention.

FIG. 14 is a flow diagram of a method of mapping a virtual environmentin accordance with embodiments of the present invention.

FIG. 15 illustrates mapping points in a map space in accordance withembodiments of the present invention.

FIG. 16 illustrates a rendering of video footage aligned with a mapped3D reconstruction of the environment within which the footage wascaptured, in accordance with embodiments of the present invention.

FIG. 17 illustrates a rendering of video footage aligned with a mapped3D reconstruction of the environment within which the footage wascaptured, in accordance with embodiments of the present invention.

FIGS. 18A-C illustrate a mapped 3D reconstruction of an environment, inaccordance with embodiments of the present invention.

FIG. 19A illustrates a mapped 3D reconstruction of an environmenttogether with indicator objects, in accordance with embodiments of thepresent invention.

FIG. 19B illustrates a mapped 3D reconstruction of an environment andaligned video footage, together with indicator objects rendered to bevisible in front of the video footage, in accordance with embodiments ofthe present invention.

FIG. 20 is a flow diagram of a method of video playback in accordancewith embodiments of the present invention.

DETAILED DESCRIPTION

An apparatus and method of video playback are disclosed. In thefollowing description, a number of specific details are presented inorder to provide a thorough understanding of the embodiments of thepresent invention. It will be apparent, however, to a person skilled inthe art that these specific details need not be employed to practice thepresent invention. Conversely, specific details known to the personskilled in the art are omitted for the purposes of clarity whereappropriate.

Entertainment Device

FIG. 1 schematically illustrates the overall system architecture of aSony® PlayStation 4® entertainment device. A system unit 10 is provided,with various peripheral devices connectable to the system unit.

The system unit 10 comprises an accelerated processing unit (APU) 20being a single chip that in turn comprises a central processing unit(CPU) 20A and a graphics processing unit (GPU) 20B.

The APU 20 has access to a random access memory (RAM) unit 22.

The APU 20 communicates with a bus 40, optionally via an I/O bridge 24,which may be a discreet component or part of the APU 20.

Connected to the bus 40 are data storage components such as a hard diskdrive 37, and a Blu-ray® drive 36 operable to access data on compatibleoptical discs 36A. Additionally the RAM unit 22 may communicate with thebus 40.

Optionally also connected to the bus 40 is an auxiliary processor 38.The auxiliary processor 38 may be provided to run or support theoperating system.

The system unit 10 communicates with peripheral devices as appropriatevia an audio/visual input port 31, an Ethernet® port 32, a Bluetooth®wireless link 33, a Wi-Fi® wireless link 34, or one or more universalserial bus (USB) ports 35. Audio and video may be output via an AVoutput 39, such as an HDMI port.

The peripheral devices may include a monoscopic or stereoscopic videocamera 41 such as the PlayStation Eye®; wand-style videogame controllers42 such as the PlayStation Move® and conventional handheld videogamecontrollers 43 such as the DualShock 4 ®; portable entertainment devices44 such as the PlayStation Portable® and PlayStation Vita®; a keyboard45 and/or a mouse 46; a media controller 47, for example in the form ofa remote control; and a headset 48. Other peripheral devices maysimilarly be considered such as a printer, or a 3D printer (not shown).

The GPU 20B, optionally in conjunction with the CPU 20A, generates videoimages and audio for output via the AV output 39. Optionally the audiomay be generated in conjunction with or instead by an audio processor(not shown).

The video and optionally the audio may be presented to a television 51.Where supported by the television, the video may be stereoscopic. Theaudio may be presented to a home cinema system 52 in one of a number offormats such as stereo, 5.1 surround sound or 7.1 surround sound. Videoand audio may likewise be presented to a head mounted display unit 53worn by a user 60.

In operation, the entertainment device defaults to an operating systemsuch as a variant of FreeBSD 9.0. The operating system may run on theCPU 20A, the auxiliary processor 38, or a mixture of the two. Theoperating system provides the user with a graphical user interface suchas the PlayStation Dynamic Menu. The menu allows the user to accessoperating system features and to select games and optionally othercontent.

Supplemented Video Recording

Referring now also to FIG. 2 , the above described entertainment device10 may operate, under suitable software instruction, as a videorecording apparatus (210A) and/or a video playback apparatus (210B) inaccordance with an embodiment of the present invention. Optionally theentertainment device may also operate as an event analyser 220, eitherseparately from the recording/playback roles or integrated with therecording role. In other implementations, the event analyser may be aremote server, and/or the video playback apparatus may be a differentform of device to the entertainment device 10, such as a mobile phone ortablet, a PC, smart TV, set-top box or different variety of videogameconsole.

Where the apparatuses are separate devices, they may communicate via theinternet (for example using Ethernet® or Wifi® ports 32, 34 asappropriate, or using cellular mobile data).

Turning now also to FIG. 3 , the video recording apparatus 210A mayoperate according to the following video recording method in which:

A first step s310 comprises recording a first sequence of video imagesoutput by a videogame. For example, the PlayStation 4 routinely saves avideo of the current video image output in a data loop that allows thelast N minutes of gameplay to be stored, where N may be for example 20minutes. Subsequently, in response to a user input, an in-game event orscheduled event, such video data can also be copied into long termstorage, such as a disk drive of the entertainment device, or a remotehost via a network, so that it is not lost when over-written in the dataloop.

A second step s320 comprises recording a sequence of depth buffer valuesfor a depth buffer used by the videogame. The depth buffer is used bythe entertainment device when calculating which parts of a virtual sceneare in front of each other and hence potentially occlude each other inthe final rendered image. As such it can provide depth data for eachpixel of the rendered image.

In one embodiment, an array of depth data of corresponding pixels of arendered image can in turn be treated as depth image.

FIG. 4A illustrates a rendered image whilst FIG. 4B illustrates thecorresponding depth buffer values.

A suitable approach for recording a sequence of depth buffer values as adepth image is described later herein.

A third step s330 comprises recording a sequence of in-game virtualcamera positions used to generate the video images. The virtual cameraposition is the position of the camera used when rendering a outputvideo image. The position can be defined as absolute positions withreference to a game world co-ordinate system, and/or relative to aglobal co-ordinate system with a predetermined origin (for example inthis latter case, the location of the virtual camera in the first outputvideo image could be set at the origin, with subsequent camera positionsbeing relative to it). Optionally, as required, additional cameraposition information may be provided, such as one or more of cameraorientation/rotation at the location, field of view, focal length,nearest drawing distance, furthest drawing distance, and the like.

The virtual camera position data may be recorded as a separate datastream or as metadata associated with the encoded depth data, asdescribed later herein, but alternatively may be recorded by encodingthe data in a different one of a plurality of image data channels notbeing used to record depth buffer values.

Also optionally, where the game is not from a first-person perspective(i.e. when the player is not also notionally at the virtual cameraposition, but has an avatar displayed on screen), then the location ofthe player and further optionally also one or more of theirorientation/rotation, speed, mode (e.g. running/walking) and/or pose maybe recorded, using the same co-ordinate scheme or schemes as used torecord the virtual video camera location data. Again this may be aseparate data steam, metadata, or encoded within an image—for exampletogether with the virtual camera data and in a similar manner.

In an embodiment of the present invention, two colour videos arerecorded; a colour video of the rendered and displayed scene asdescribed previously, and also a colour video encoding the 16-bit depthdata, typically based on one of the following formats:

-   -   An H.265 video using the Main 4:4:4 16 Intra profile in 4:0:0        monochrome at a bit depth of 16 bits, or    -   An H.265 video using the Main 4:4:4 16 Intra profile in 4:4:4        chroma sampling at a bit depth of 16 bits, or    -   A video in a similar format such as High Throughput 4:4:4 16        Intra profile in 4:0:0 or 4:4:4 at 16 bits,        for example in any HEVC version supporting these profiles, or        equivalent coding schemes, and/or    -   A UCL colour video, in which the 16-bit depth buffer is        converted to three colour channels (e.g. RGB values), which can        then be stored like a normal video using h264, AV9, h265 and the        like.

The UCL colour video enables resilient compression of the depth data(treated as colour data), as explained in relation to live-action videowithin Fabrizio Pece, Jan Kautz, and Tim Weyrich; ‘Adapting StandardVideo Codecs for Depth Streaming’, Joint Virtual Reality Conference ofEuroVR—EGVE (2011), Editors R. Blach, S. Coquillart, M. D'Cruz, A.Steed, and G. Welch, the contents of which is incorporated herein byreference.

In summary, in a UCL colour video format the top 8 bits of a firstcolour channel are a linear mapping from the 16 bit depth data, toprovide an approximate depth value. The second and third colour channelsare then mappings (e.g. triangle waves) also applied to the 16 bit depthdata and having a period at least twice the quantisation level of thedepth data (e.g. for an 8-bit depth having 256 levels, the period wouldbe ≤512), but with different phases. Due to the phase difference, theyencode complementary high resolution depth information with respect tothe spatial period of the function. The depth information can then berecovered by reversing the mapping in the first channel to provide arough depth value, and then reversing the mapping of typically one ofthe second and third channels, depending on the value from the firstchannel, to obtain a relative depth value by which to adjust the roughvalue.

In another format that may be similarly considered, the 16 bit depthdata is compressed to 8 bits in a lossy fashion, and stored in the top 8bits of a first colour channel. Then a first correction layer (e.g. thedifference between the original depth layer and a decompressed versionfor the data in the first colour channel) is stored in the top 8 bits ofthe second colour channel. Finally, a second correction layer (e.g. thedifference between the original depth layer and a decompressed versionfor the data in the first colour channel as corrected using thecorrection layer) is stored in the top 8 bits of the third colourchannel. Alternatively correction data for a single correction step canbe stored between both the second and third colour channels in theirrespective top 8 bits.

Put another way, in either format the first channel of 8 bits provides arough but global depth value, whilst the second and third channels of 8bits provide higher resolution depth information to adjust the roughestimate.

Also in either case, where the video codec comprises for example a 10bit colour depth, then the 8 bits in each channel are even more robustto video compression.

Notably therefore in either case the 16 bits of the original depth dataare stored as 24 bits of encoded depth data within a host data scheme(such as RGB data or similar such as YUV, YCoCg, YCbCr and the like),and preferably those bits do not include at least the lowest significantbit of the host data scheme—although it will be appreciated that someschemes allocate a different number of bits to different channels and sooptionally, but less preferably, at least one but not all channels maybe fully occupied by encoded depth data. Of course, if potential errorsin depth information can be accepted, or the anticipated compressionscheme will not affect bit values (or only to a degree that is visuallyacceptable), then the encoded depth data may occupy all the respectivebits of some or all of the colour channels.

Notably whilst the above summary refers to colour channels, in somecolour encoding schemes not all channels correspond to a colour per se(for example a channel may indicate luminance); however in each case thescheme as a whole serves to define a point in a colour space, and it isin this sense that the channels are referred to herein as colourchannels, or equally as colour-space-descriptor channels.

It will be appreciated that 16 bits of depth data, and compression to 8bits, in three channels, are all exemplary only. More generally in a UCLcolour video, N-bit depth data (where N is typically 16) may be encodedto M bits (where M is typically 8) per colour-space-descriptor channel,and typically M<P, where P is the native bit depth of the respectivechannel in the host data scheme, and M is preferably 1 bit, or morepreferably two bits, fewer than P. The number of colour channels used istypically three (e.g. YUV), but may be different (e.g. CMYK).

Hence more generally encoding the depth buffer value sequence comprisesencoding depth data of a first bit depth across a plurality of thecolour space descriptor channels used by a selected video scheme, suchthat a first channel encodes data indicative of depth to a first levelof accuracy, and the or each subsequent channel encodes data that, inconjunction with the data of the first channel, is indicative of depthto a second, higher level. Typically, during this encoding the depthdata in each channel is then encoded to a bit length shorter than thebit length of the respective channel, although this is not essential.

Accordingly, both the colour video of the rendered environment and thecolour-encoded video of the depth data can both be encoded and/orcompressed by a conventional video coding technique such as h.265, forexample so as to be streamed to one or more viewers, and thequantisation of the depth information will typically be preserved in amanner as robust (or more) than that of the colour data in the renderedvideo.

Optionally to provide ease of transmission and synchronisation, the twovideos may be encoded as a stereoscopic pair (despite not being so).

A fourth step s340 comprises recording one or more in-game events andtheir respective in-game positions, using a similar scheme to that forthe virtual camera location and optional player location. The choice ofwhat in-game events to record in this manner will be made by a designer,but may typically include one or more of crashes/character deaths,overtaking/beating a real or computer based opponent, changing anin-game state of the user (e.g. changing equipped weapons or the like,or engaging a nitrox boost in a car), and player choices (such asturning left or right to avoid an obstacle, or electing to jump overit). In this latter case, the choice may be associated with apredetermined in-game decision point that may be location based (e.g. anobstacle or path choice) or may be logical (e.g. when navigating adialog tree with an in-game character). In the case of a location basedchoice, due to user variability regarding when they respond to thechoice, the choice made may be associated with the position of thein-game decision point rather than the position of the user or camera,to assist with subsequent analysis of the decision. Alternatively or inaddition, such a decision may be encoded when made by the user, or whenthe in-game decision point is at the nearest draw position with respectto the virtual camera, or at some other predetermined relationship withthe virtual camera (for example within a predetermined distance) so asto provide predictability as to which video image may be associated withthe choice data, or the choice data may be encoded for each imagebetween these two moments (or similarly for any video frame where thecamera and/or user avatar are within a predetermined distance of thein-game decision point). In addition to location specific events,on-going events may also be recorded. Hence optionally for each videoimage, the current user input or inputs (e.g. buttons pressed, orassociated input values) may also be recorded in a similar manner toprovide an approximate record of the user's interactions with the game,and similarly the user's in-game position (e.g. avatar positon) may betreated as an ongoing event if different from the camera positon. As isnoted later herein, whilst this recording step typically occurs duringgame play and reflects events arising directly from game play,alternatively or in addition the recording step for such in-game eventsmay occur after the video images and other data have been output, andoptionally after they have been broadcast/streamed; that is to say, aviewer subsequently watching the video using a viewer compatible withthe techniques herein with have sufficient information available todefine their own in-game events after the fact. These may then beshared, e.g. by reposting the updated video, or by transmitting them toa central server, as appropriate and as described later herein.

As is noted above, the data is recorded for each of a sequence of videoimages output by the videogame, but generally is not recorded as part ofthe sequence of output video images itself but instead is recorded as aparallel sequence of data with at least the depth data encoded as videoimages.

In the preferred colour video encoding approach, the other informationdescribed herein as being encoded within a colour data channel, such asthe virtual camera position, and optionally an avatar position and/orin-game event positions, may be stored as a separate data stream withinthe colour encoded depth video (or potentially within the video of therendered output, or potentially in both to provide redundancy, or acrossboth the reduce or balance individual overheads, for example to assistwith synchronous streaming of the videos).

For example, this data may be stored in one or more extensible metadataplatform streams or similar, respectively associated with one the twovideos. Alternatively the selected video scheme may comprise user fieldsthat may accommodate this data.

Hence in a fifth step S350, the depth buffer value sequence is encodedas a second sequence of video images; and in a sixth step S360, thein-game virtual camera position sequence is associated with at least oneof the first and second sequence of video images (typically the secondsequence of video images).

In a further optional step, an identifier for the videogame is alsoassociated with one or both video image sequences (together with any ofthe optional additional information also encoded, such as playerposition, user choices and the like).

The identifier enables subsequent analysis of the video sequence withoutthe need for image-based recognition of the game from which the videosequence has been recorded. The identifier may simply be the name of thegame in plain text, or a unique issue number associated with the game.For simplicity, the identifier may correspond to an identifier alreadyassociated with the game, for example for the purposes of registeringownership of the game with an administrative service associated with thehost videogame console.

Optionally one or more in-game events and their respective in-gamepositions are associated with the identifier for the videogame.

The in-game events, their respective in-game positions, and theidentifier for the videogame may then optionally be uploaded to a remoteserver operable as the event analyser 220, which receives such data froma plurality of client devices acting as video recording apparatuses, andidentifies statistically significant features of the data, as describedlater herein.

The in-game events and their respective in-game positions mayalternatively or in addition be encoded along with the depth buffervalue sequence, the in-game virtual camera position sequence, and theidentifier for the videogame within a colour channel of thesupplementary image sequence, thereby (also) associating them with theidentifier for the videogame in this manner. This allows the specificinstance of the in-game events to be associated with the specific videorecording.

Optionally, each recorded image sequence of a videogame (videorecording) may have a unique video ID, which may optionally betransmitted to the event analyser. The event data may then betransmitted to the event analyser in association with the unique videoID. Subsequently the event analyser may then optionally transmit theevent data, in addition to any statistical analyses, back to a videoplayback device that transmits the unique video ID to it.

Similarly optionally the depth buffer value sequence and/or the in-gamevirtual camera position sequence and any of the other optional data(such as player avatar positon) could also be uploaded to the eventanalyser in association with the unique video ID.

If all the supplementary data is uploaded in this fashion, it may beprovided to the server as a parallel video recording encoded asdescribed previously herein, or as the separate data elements for theserver to encode in this manner.

Subsequently when a video playback device transmits the unique video IDfound in a video recording, it can receive all of the supplementarydata, for example as a parallel video recording encoded as describedpreviously herein.

Alternatively or in addition, the video recorder could upload theparallel video recording to an online host (such as YouTube® or Twitch®)first, obtain the URL associated with the hosted recording, and embedthis URL in a user field of the video recording of the game before alsouploading that to the online host. Equivalently, after uploading theparallel video recording to the on-line host, using the unique video IDas the video name, the video recorder could embed the video ID in theuser field of the video recording to be subsequently used as a searchterm with the on-line host.

In either case, as long as the unique video ID or URL remains associatedwith the original video (for example in a user field of the video), thena video playback device adapted to implement techniques disclosed hereincan access the desired supplementary data either by requesting it fromto the event analyser or accessing the parallel hosted video from anon-line host, whilst the video itself remains otherwise conventional andable to be handled and transmitted by conventional or legacy devices andapplications without special regard to also handling and transmittingnon-standard supplementary data relating to these techniques.

Supplemented Video Playback

Turning now to FIG. 5 , the video playback apparatus 210B may operateaccording to the following video playback method in which:

A first step s610 comprises obtaining a first video recording of avideogame playing session, comprising a sequence of video images. Thismay be done by any suitable means, such as downloading a video file,streaming a video stream for a web service such as YouTube® or Twitch®,or accessing a video recording already in a local memory (such as an HDD37 or BD ROM 36/36A) of the playback apparatus.

A second step s620 comprises obtaining a second video recordinggenerated by encoding a depth buffer value sequence (such as the H.265and UCL examples herein).

A third step s630 comprises obtaining an in-game virtual camera positionsequence associated with at least one of the obtained video recordings,for example as a data file provided with a video recording, or ametadata extension, or a user field. Optionally additional data such asavatar positions and in-game event data may also be included.

Alternatively such a parallel video recording comprising encoded data,and/or one or more of the other data sequences (camera position, avatarposition, event position etc.), may be accessed by reference to a uniquevideo ID obtained from a data field of a received video recording andsubmitted to the event analyser server, or alternatively by reference toa URL or search term obtained from a data field of a received videorecording that is used to access the data from a data hosting service.

It will be appreciated that the supplementary data may be downloaded inits entirety, or alternatively streamed at the same rate as the videorecording of the videogame (and as applicable the depth data video) sothat the supplementary data is provided in a just-in-time manner.Optionally the supplementary data may be streamed with a predeterminedframe offset (for example 1, 2, 3 or more frames in advance relative tothe video recording of the videogame) to provide sufficient processingtime to have processed information ready for reception of thecorresponding video frame of the videogame, and/or to provide anysmoothing, averaging or error correction functions for supplementarydata that would depend upon receipt of subsequent frames ofsupplementary data. This could be achieved by padding the videorecording of the videogame with the desired predetermined number ofblank frames at its start, or delaying playback of the video recordingof the videogame by the desired predetermined number of frames. Such aprocessing time offset may also optionally implemented if encoding thegame footage and depth video as a stereoscopic pair, so that the depthvideo is a predetermined one or more frames in advance of the gamefootage.

As noted above, optionally in-game event data may be obtained at thisstage, thereby subsequently allowing augmentation (e.g. displaying apath taken, or a user comment) responsive to that in-game event byitself.

However, alternatively or in addition, an optional further step S635comprises obtaining data indicative of a statistically significantin-game event and an in-game event position. As described elsewhereherein, this data is obtained from the event analyser, either as a file,or streamed to the video player during playback. The data typicallycomprises data indicative of the in-game event analysis data, e.g. datarelating to the significance of the event and optionally otherstatistical data (and typically also the type of event, etc., to assistwith selecting how to graphically represent the event).

As was noted previously, the choice of what in-game events have beenrecorded may have been made by designer and may include one or more ofcrashes, character deaths, overtaking or beating an opponent or indeedbeing overtaken or beaten by an opponent, changing the in-game state ofthe user, player choices and/or player inputs. As noted above,augmentations based upon these events per se may be provided. However,optionally this data may be analysed as described elsewhere herein, anddata relating to this analysis may then be associated with the eventlocation.

If the data is subsequently downloaded as a file in advance of videoplayback displaying a particular in-game location, then the eventlocation may be used to decide when to use the event analysis data,whereas alternatively or in addition when the data is subsequentlystreamed in synchronisation with playback of a recording of thevideogame, then the event analysis data may be streamed according towhen the recording of the videogame reaches the event location,optionally in terms of a predetermined offset from the camera positionor optionally from the player avatar position for that moment in therecording.

A fourth step S640 then comprises calculating a position within acurrent video image of the first video recording (the game footage)corresponding to the in-game event position, in dependence upon theassociated in-game virtual camera position and decoded depth buffervalues obtained from the second, depth video.

Hence if for the currently displayed video image of the videogame theposition of the camera using the in-game or global co-ordinate system isknown, and the depth data of the pixels in the display video image areknown or can be interpolated from the associated depth data, then ineffect the in game or global (X, Y, Z) coordinate of each pixel in thecurrently displayed video image of the videogame can be determined.Accordingly, the position of the in game event within the currentlydisplayed video image can be determined.

In particular, if for a given event, the corresponding X, Y coordinatein the currently display video image is determined to have a Zcoordinate that is closer than the Z coordinate of the event, then ineffect the event is obscured from the current viewpoint of the displayvideo image by an object within the virtual environment depicted withinthe video image.

Using this information, at a fifth step s650 a video playback device canaugment the current video image with a graphical representation of an ingame event, responsive to the calculated position. In particular thevideo playback device can decide whether or not to occlude some or allof a graphical representation of the in game event based on whetherelements of the displayed environment are currently in between the gameevent location and the viewpoint presented by the video. For example,the video playback device may prepare for rendering a simple polygonbased object such as a tetrahedron, acting as a pointer, and then usethe Z values of the video image to perform a so-called z-culling on thetetrahedron in a final render so that the tetrahedron appears to benaturally embedded within the environment of the video, being occludedas suitable from the current viewpoint of the virtual camera thatrecorded the video image. Hence the technique may comprise calculating,in dependence upon the depth buffer values, any occlusion of thegraphical representation at the calculated position caused by foregroundelements of the video image.

The playback device may not augment every obtained in-game event. Forexample, the viewer may be able to toggle which event types to display,or set an event threshold (for example, only show an event that add morethan a threshold value to the score). Similarly, the playback device mayalso show statistically significant in-events or a subset, or only showstatistically significant events or a subset, depending on playbacksettings.

FIG. 6 illustrates this augmentation for the example video image of FIG.4A. In this figure, paths of other players (for example particularlyfast or slow players in red or blue tracks respectively) are shown. Fora greyscale reproduction, the specific meaning of each track is notnecessary to an understanding of the invention. Notably, as seen in theexpanded section, the tracks disappear behind features of theenvironment as the Z position of the track data exceeds the Z positionof the features within the video image.

FIG. 6 also shows simple polygon objects (in this case tetrahedra)indicating events such as vehicle skids or braking. It will beappreciated that more elaborate, visually appealing and informativeindicator objects, optionally with textures of their own, may be usedfor this purpose, and that typically a different respective graphicalrepresentation will be used for corresponding different event types. Itwill be appreciated that other graphical effects may be applied, such asreducing the brightness of video pixels whose x,y,z position intersectsa line in a predetermined direction from an indicator object, therebycreating an apparent shadow of the indicator object within the videoedgame environment, and so improving the apparent immersion of theindicator object. Similarly, the video playback device may analyse theeffective resolution or compression rate of the video, and degrade theeffective resolution of the indicator object to substantially match this(for example by pixelating and/or blurring the rendered object), so thatthe indicator object appears to be more part of the background videoimage.

Optionally, the video playback device can also obtain an in-game playerposition sequence associated with the video recording. Again asdescribed previously this can be in a separate file or stream or encodedwithin a parallel image sequence. The augmenting stage may then comprisedisplaying a relationship between the current player position in thevideo and one or more event positions. This may variously take the formof indicating distance/countdown values between the player position andthe event position, adding a line, arrow or path between the playerposition and the event position, only showing or fading in the indicatorobject associated with an event when the distance between the playerposition and the event position are within a predetermined threshold,and the like.

Turning now to FIG. 7 , the server operating as an event analyser 220may operate according to the following event analysis method, in which:

A first step S810 comprises respectively receiving, from a plurality ofvideogame devices (acting as video recording apparatuses), a videogameidentifier and one or more associated in-game events and theirrespective in-game positions. Hence as described previously herein, theevent analyser receives data relating to a particular videogame thatidentifies in-game events, and where they occur within the game, from aplurality of videogame devices.

As noted previously herein, optionally the event analyser may receiveany of the other supplementary data recorded by a video recordingapparatus, together with a unique video recording ID.

A second step S820 then comprises performing an analysis on one or moreaspects of the in-game events associated with a videogame identifier,and their respective in-game positions, to identify statisticallysignificant in-game events.

This may be done for example by performing a geospatial analysis of aplurality of events of a similar kind to identify hotspots, cold spotsand other group statistics indicative of the behaviour of a corpus ofplayers for that kind of event, or for a particular instance of an eventat a particular position.

An aspect of significance for an event can be selected by weighting forit. Hence for example a set of points in game space relating to whereusers applies the brakes in a racing game can be weighted according tothe respective eventual lap times associated with each point.

The analysis then generates a z-score for each point separately (e.g.which reflects how many neighbours also had high weights), and ap-value, indicating if this point is an anomaly.

These analyses can be performed for a particular game titleperiodically, and/or in response to receiving more data for that game(for example after receiving 1, 10, 100, 1,000, 10,000 or 100,000additional datasets, as appropriate).

It will be appreciated that different aspects of an event or event typecan be analysed separately in this fashion depending on the weightingused. For example, braking events could be analysed with respect to laptimes or whether or not the lap was completed, vehicle types, or userdemographics.

To this end, it will be appreciated that other information about gameplay may also be recorded by the video recording apparatus, which may bereferred to as session data; i.e. not events within the game play perse, but information about the game play, such as difficulty setting,player skill level or equipment used, final outcomes (times, scores,achievements, rankings or the like) determined after completion of alevel, and so-on. In the event that only part of a level is videorecorded, the video recording apparatus can thus optionally append suchdata to the video recording once a level (or other logical point atwhich to obtain such values) is reached, even if the video recordingitself has ceased. Such session data may be stored as a separate file orencoded in any suitable manner within the game video recording orparallel video recording. For example, the session data may be includedas one or more frames at the beginning or end of the parallel videorecording.

Alternatively or in addition to such geospatial analysis, auser—generated event marker or user ID may be associated with aparticular uploaded set of event data.

This allows the event analyser to provide event data corresponding tospecific individuals, such as for example players found on a user'sfriend list associated with their own user ID. In this way,alternatively or in addition to statistical analyses of a wider corpusof players, individual choices and events from friends of the viewer ofthe playback may be shown as an augmentation of the video, and/or ageospatial analysis restricted to just their friendship group.

This principle could also be extended to clans, teams and otherself-identified groups though user-generated markers, so that forexample e-sports teams could augment a video posted by a competitor withjust an overlay of their performance data.

Expanding further, the geospatial analysis can be performed multipletimes for different corpora of players, to provide analyses based onlocation (e.g. national stats) and demographics, such as age and gender.Such information is generally available from the registration detailsheld in association with each user ID.

In any event, subsequent to the analysis, a third step S830 comprisesreceiving, from a video playback device, a videogame identifier and atleast one of an in-game virtual camera position and an in-game playerposition.

Hence in addition to receiving data from video recording apparatuses,the event analysis server also receives data requests from one or morevideo playback apparatuses. The requests identify the videogame in thevideo so that the event analyser knows what data set to reference(although this may be implicit, for example when an event analysisserver is dedicated to supporting only one game, then the act of sendinga request to that server constitutes identification of the relevantvideogame and data set).

The requests also include at least one of an in-game virtual cameraposition and an in-game player position. Depending on how the data istransmitted back to the video playback apparatuses, this can takedifferent forms. If data for an entire level (or segment/branch etc. ofa level or region) is to be downloaded, then identification of the levelserves to identify the position of the camera/player to the extentneeded to acquire relevant data.

Meanwhile if the data is being streamed, then the current position ofthe camera/player corresponding to a displayed frame of the video stream(or optionally a predetermined number of frames ahead, to account foraccess and network latency) may be used. This allows the received datastream to track the progress of events within the video, which arelikely to differ between individual videos due to how each user playsthe game, and what events they experience (such as a car crash orbreakdown instead of smooth driving) that would otherwise makeprediction of what events are relevant to the current video displaydifficult.

It will be appreciated that in between position updates on aonce-per-level and every-frame basis, a number of schemes may be adoptedwithin the technique, such as time or distance based periodic updates ofposition (e.g. every N seconds or M metres, where N or M arepredetermined values). Optionally, triggers may be encoded within thevideo itself (e.g. a flag or value in a user field) by the videorecording apparatus, corresponding to when events occurred during gameplay, so that when these are encountered during playback then thecorresponding camera or player location is transmitted to the eventanalyser in order to receive data about the corresponding event.

In any event, in response then in a step fourth step S840 the eventanalysis server selects analysis data relating to one or more identifiedstatistically significant in-game events associated with the receivedvideogame identifier and having an in-game position within apredetermined distance of at least one received position (as notedabove, corresponding to a level, periodic time or distance, or currentor impending video frame). The predetermined distance may be the drawdistance of the videogame, so that an indicator object for the event canappear as if it is part of the in-game render, but in principle may beany predetermined distance from the received position.

The selection of analysis data may follow one or more principles. Forexample, data that has the greatest significance for an event may bechosen (for example, if users are presented with a choice to turn leftor right, and 95% of players who turn right complete the level whilst95% of player who turn left to not, then this aspect of the decisionevent is more significant than whether 60% of cars turn right and 60% ofmotorbikes turn left). Alternatively, data that relates to the apparentchoice/event of the player in the video may be preferentially selected.Similarly, data that relates to preferences set by the viewer of thevideo may be chosen, such as looking for the most common events, or theleast common events, or preferred events such as crashes, but notovertaking.

Finally, in a fifth step S850 the event analysis server transmittingdata indicative of the in-game event analysis data and its in-gameposition to the video playback apparatus. Then as noted previously, thevideo playback apparatus can use the data to construct an augmentationlayer for the video, as illustrated in FIG. 6 .

It will be appreciated that because the location of in-game events isitself constrained by the rules and environment of the game, thecumulative event data received by the event analysis server will beconsistent for that game (e.g. all events related to overtaking will beon positions corresponding to the race track, or at least to positionswhere overtaking is legal within the game). As a result, the locationsassociated with event analysis data and the locations associated withthe camera/player within the current video will be consistent with eachother and the game environment within the video (as per FIG. 6 ), andhence appear to interact naturally even though the event analysis serverand the video playback apparatus may not have any explicitknowledge/model of the actual virtual environment within the game.

It will be appreciated that in principle a videogame console couldoperate as both a video recording apparatus and a video playbackapparatus, so that a user could review their own play almost immediatelywith the benefit of statistical event data overlaid on top. Furthermore,a videogame console could in principle also operate as an event analysisserver, for example analysing historical records of play by one user,such as a professional e-sports player, to assist them in identifyingtrends in their play.

Variants of Recording and Playback

Variations of the above techniques can also be envisaged.

The use of the received analysis data can vary to suit the style of thegame that has been videoed. For example, providing a commentary thatsimply says whether a player took the popular or unpopular choice atcertain points in-game may be applicable in some cases, whilst a lot ofgraphically complex statistics relating to the positions of multipleplayers may be appropriate in another game.

Similarly, the event analysis server may provide graphical data(indicator geometries, textures etc.) in response to the receivevideogame identifier, so that the video playback apparatus has graphicsassets to highlight events that are graphically in keeping with thatparticular game in the video (since the video playback apparatus may nothave the game installed itself and may have no information about it orassets for it).

Whilst the description refers to use of a parallel video recording ofdepth data, and suggests that camera and event data etc., is alsoencoded within a data channel of that parallel video recording, inprinciple such data could be included within user data fields of a videocodec that supported such fields, so that some or all of the data wasdirectly included with the video recording of the game play. This may bean option where the videos are hosted by a non-legacy service that hasbeen adapted to accommodate the present techniques (for example byretaining such data fields, or not applying lossy compression to them).

The techniques described herein enable the overlay of paths taken bydifferent players (e.g. as shown in FIG. 6 ), and other information, ona race track or any other traversable virtual environment, using thedepth buffer and in-game virtual camera positions to display these withthe appropriate depth.

It will be appreciated that these techniques may facilitate theaugmentation of video-recordings of game play for a number of uses. Forexample, graphics providing commentary and analysis may be overlaid ontop of e-sports coverage.

Other examples include that a user can add a virtual object to a replayof a user's video. The virtual object may be, for example, a marker or amessage in the form of a 3D callout with text. Typically, the userdefines an after-the-fact in-game event for which a virtual object orgraphical effect is provided.

For example, on watching back a video of a player completing a racetrack, a viewer might leave a message like “awesome jump!” at the pointwhere the player makes the jump, or indicating the peak height of thejump, as shown in FIG. 8 . Where an object chosen to indicate such anevent is itself 3D, they may thus have a position and orientation thatis consistent with the environment within the video, so that they appearas if part of the originally captured footage. An example is of an arrowset by the original player or a subsequent viewer of the video thatpoints to hidden treasure, as shown in FIG. 9 .

In another example, a player or viewer might have the option ofdisplaying a ‘death zone’ option. The ‘death zone’ might appear as ashaded volume of space within the virtual environment (illustrated by ahatched area in FIG. 10 ), and represent the area within the map wheremost players are killed. During gameplay, the depth data stored in thedepth video can be used to render the death zone so that it appears withthe correct depth for the current view of the environment. This might beswitched on by a spectator watching that player play the game (forexample in e-sports).

In another example, in a manner similar to that shown in relation toFIG. 6 , the virtual object might be a path taken by successful players.In another example, the virtual objects could be an indicator indicatingthe position of e.g. enemies in the game. In yet another example, thevirtual object could indicate the effective range of a weapon (seen inFIG. 11 as a colour-coded strip indicating weapon effectiveness into thedistance). Spectators of e-sports might want to turn these on, forexample, to see where the enemies where when a player was killed.

Hence it will be appreciated more generally that in principle whilstin-game events may be recorded during play for the purposes ofaugmenting the video, more generally game events and hence virtualobjects or graphical effects may be associated with the recording afterthe recording has been generated (either offline or live), and treatedin an identical fashion to in game events recorded during play asanother possible augmentation data source or layer.

It will be appreciated therefore that a video viewer compatible with theparallel data sets of video, depth and camera position can calculatewhere to define an additional in game event (such as one of thecomments, objects, or regions or other overlays noted above) within therecording, after the recording has been made and output by the originalplayer, based on where a user chooses to place the game event within thecurrent image; this x, y position in turn corresponds to a depth value(distance) from the camera viewpoint in the respective video image, thusallowing it to be defined with respect to the same reference point asthe camera itself (e.g. in a similar manner to other in-game event data)within the associated data.

It will be appreciated that whilst reference is made herein to ‘videorecordings’ and ‘sequences of video images’, these encompass bothpre-recorded video (e.g. uploaded to a web-based host or streamingserver) and also live video (again for example uploaded to a streamingserver). In either case, the ability to augment the obtained footage isbased on the combination of the video recording of the game footage andalso the parallel recording of depth data and camera data.

Hence for example a streaming game service such as PS NOW® could outputboth colour video and depth encoding video, which could be used forrendering virtual objects within the live game. For example a secondplayer on a local console could participate by augmenting and/orvisually narrating the first player's experience.

Hardware for Recording and Playback

It will be appreciated that the methods described herein may be carriedout on conventional hardware suitably adapted as applicable by softwareinstruction or by the inclusion or substitution of dedicated hardware.

Thus the required adaptation to existing parts of a conventionalequivalent device may be implemented in the form of a computer programproduct comprising processor implementable instructions stored on anon-transitory machine-readable medium such as a floppy disk, opticaldisk, hard disk, PROM, RAM, flash memory or any combination of these orother storage media, or realised in hardware as an ASIC (applicationspecific integrated circuit) or an FPGA (field programmable gate array)or other configurable circuit suitable to use in adapting theconventional equivalent device. Separately, such a computer program maybe transmitted via data signals on a network such as an Ethernet, awireless network, the Internet, or any combination of these or othernetworks.

The hardware for the video recording apparatus may thus be aconventional computing device such as a PlayStation 4 operating undersuitable software instruction, comprising a recording processor (e.g.CPU 20A operating under suitable software instruction) adapted to recorda first sequence of video image output by a videogame to a video storagemeans (e.g. HDD 37), the recording processor being adapted (e.g. bysuitable software instruction) to record a sequence of depth buffervalues for a depth buffer used by the videogame, the recording processorbeing adapted (e.g. by suitable software instruction) to record asequence of in-game virtual camera positions used to generate the videoimages, and the recording processor being adapted (e.g. by suitablesoftware instruction) to record one or more in-game events and theirrespective in-game positions; a video generating processor (e.g. CPU 20Aagain operating under suitable software instruction) adapted to generatea second sequence of video images encoding the depth buffer valuesequence; and an association processor being adapted (e.g. by suitablesoftware instruction) to associate the in-game virtual camera positionsequence with at least one of the first and second sequence of videoimages. In each case, the suitable software instructions implementmethods and techniques described herein as appropriate.

Similarly, the hardware for the video playback apparatus may be aconventional computing device such as a PlayStation 4 operating undersuitable software instruction, comprising a playback processor (e.g. CPU20A operating under suitable software instruction) adapted to obtain afirst video recording of a videogame playing session, comprising asequence of video images, the playback processor being adapted (e.g. bysuitable software instruction) to obtain a second video recordinggenerated by encoding a depth buffer value sequence, the playbackprocessor being adapted to obtain an in-game virtual camera positionsequence that is associated with at least one of the obtained videorecordings; an analysis processor adapted (e.g. CPU 20A operating undersuitable software instruction) to provide an in-game virtual cameraposition to an event analyser, the analysis processor being adapted(e.g. by suitable software instruction) to obtain data indicative of astatistically significant in-game event and an in-game event position; aposition calculation processor (e.g. CPU 20A operating under suitablesoftware instruction) adapted to calculate a position within a currentvideo image of the first video recording corresponding to the in-gameevent position, in dependence upon the associated in-game virtual cameraposition and decoded depth buffer values; and an augmentation processor(e.g. CPU 20A and/or GPU 20B operating under suitable softwareinstruction) adapted to augment the current video image with a graphicalrepresentation of the statistically significant in-game event,responsive to the calculated position. Again in each case, the suitablesoftware instructions implement methods and techniques described hereinas appropriate.

Finally likewise an event analyser may be a conventional computingdevice such as a server or a PlayStation 4 operating under suitablesoftware instruction, comprising a receiver (e.g. Ethernet® port 32operating in conjunction with CPU 20A under suitable softwareinstruction) adapted to respectively receive, from a plurality of videorecording apparatuses, a videogame identifier and one or more associatedin-game events and their respective in-game positions; an analysisprocessor (e.g. CPU 20A operating under suitable software instruction)adapted to perform an analysis on one or more aspects of the in-gameevents associated with a videogame identifier, and their respectivein-game positions, to identify statistically significant in-game events;the receiver being adapted to subsequently receive, from a videoplayback apparatus, a videogame identifier and at least one of anin-game virtual camera position and an in-game player position; aselection processor (e.g. CPU 20A operating under suitable softwareinstruction) adapted to select one or more identified statisticallysignificant in-game events associated with the received videogameidentifier and having an in-game position within a predetermineddistance of at least one received position; and a transmitter (e.g.Ethernet® port 32 operating in conjunction with CPU 20A under suitablesoftware instruction) adapted to transmit data indicative of the in-gameevent and its in-game position to the video playback device. Again ineach case, the suitable software instructions implement methods andtechniques described herein as appropriate.

As noted previously, the video recording apparatus, video playbackapparatus and event analyser may be three separate devices, or maybe twoseparate devices in any combination, or a single device comprising allthree aspects.

Consequently a system (200) may comprise the video recording apparatusas described herein, and one or more of video playback apparatus and theevent analyser either as separate devices or within a single device. Inprinciple a system may similarly comprise the video playback apparatusas described herein together with the event analyser.

It will be appreciated that using the above techniques and apparatus, afacility is provided wherein users can record their own gameplay andupload it to publicly accessible hosts such as YouTube® and Twitch® (orpotentially a proprietary host such as one belonging to theadministrator of a network associated with a type of videogame console),and subsequently viewers of that video, using a device or applicationimplementing as applicable the techniques described herein, can watchthe video of the user playing the game that is augmented withinformation relating to how other players played the game, therebycreating a context for the users decisions, successes and failureswithin the game, and a more rich viewing experience.

2D Mapping

As described previously herein, a useful source of information for boththe player of the game and potentially the watcher of a video recordingof that game is a map relating to the users experience of the game orsimilarly the video recording of the game.

Turning now to FIG. 12 , to address or mitigate this issue, a method ofmapping a virtual environment (such as the game environments illustratedin FIGS. 4A, 6, 8, and 9-11 ), comprises:

In a first step s1310, obtaining a first sequence of video images outputby a videogame title, for example as described previously herein eitherby accessing image data directly from the entertainment device whilerunning a game, or from a video recording thereof, generated asdescribed herein.

In a second step s1320, obtaining a corresponding sequence of in-gamevirtual camera positions at which the video images were created, forexample as described previously herein either by accessing the relevantdata directly from the entertainment device while running a game, orfrom a video recording of the output images thereof, or from dataassociated with the video recording, or from data embedded in a separatevideo recording also comprising depth information, or any other suitablemeans that serves to associate the virtual camera position with thecorresponding video image.

In a third step s1330, obtaining a corresponding sequence of depthbuffer values for a depth buffer used by the videogame whilst creatingthe video images, for example as described previously herein either byaccessing the relevant depth buffer data directly from the entertainmentdevice while running a game, or from data associated with a videorecording of the output images thereof, for example in the form of aseparate data file or second video recording that serves to encode thedepth data using any appropriate techniques such as those describedherein.

Then in a fourth step s1340, for each of a plurality of video images andcorresponding depth buffer values of the obtained sequences,

a sub-step s1342 comprises obtaining mapping points corresponding to aselected predetermined set of depth values corresponding to apredetermined set of positions within a respective video image; whereinfor each pair of depth values and video image positions, a mapping pointhas a distance from the virtual camera position based upon the depthvalue, and a position based upon the relative positions of the virtualcamera and the respective video image position.

Mapping points may be obtained by calculating a map positioncorresponding to the distance and direction of the map point, with thedirection being based upon the difference between the optical centre ofthe virtual camera and a respective selected position within a videoimage, and the distance being based upon the virtual camera position andthe depth value corresponding to the selected position within the videoimage.

FIGS. 13A-C illustrates process for a predetermined set of positionscomprising the pixels of the centreline of an image. In FIG. 13A,greyscale image elements, if shown, would correspond to depth valueswith more distant values being darker. It will be appreciated that theprecise nature of these elements is not important to an understanding ofthe invention. For example, if shown according to a differentconvention, then the closest depth values (e.g. a value of zero) mayappear darkest. As noted above, the predetermined set of positions 1410is a set of pixels along the centreline of the image. The set may sampleall or a subset of pixels, and hence for example may comprise every Npixels, where N may, as a non-limiting example, be 1, 2, 3, . . . 10,etc.

The upper circle 1420 indicates the current virtual camera position, andthe lower circle 1430 indicates the virtual camera position in the caseof a 2D mapping (e.g. with elevation set to zero, or equivalentlysubtracting the current level of the virtual ground at the location ofthe virtual camera). In this example, the field of view of the virtualcamera is indicated by the angle between the two lines emanating fromeach of the circles.

As shown in FIG. 13B, the corresponding depth value for each pixel inthe predetermined set is obtained. It will be appreciated that where theresolution of the depth value information is less than the imageresolution, then a regular sampling every N pixels corresponding to theeffective resolution of the depth information may be used instead.

As shown in FIG. 13C, the map points may then be identified in a mapspace 1450, based upon the relative position of the sample pixel withinthe image and the position of the virtual camera, together with theobtained depth value.

Typically the map is generated with respect to the origin of an in-gamecoordinate system. Consequently, a map point may be calculated for themap based on the position of the virtual camera in the game coordinatesystem together with the distance and direction from the virtual cameraas indicated by the depth value and the pixel position within the imagecaptured by the virtual camera.

The calculated direction may further take account of the field of viewof the virtual camera. Virtual cameras with different fields of view mayresult in the same pixel position within an image corresponding to adifferent angle away from the optical axis of the virtual camera.Alternatively, the field of view may be fixed or assumed, and/or theeffect of the field of view imposes a scaling factor within thecalculations that can be ignored for the purposes of generating a map.

Similarly the calculated direction may further take account of theorientation of the virtual camera, so that the apparent direction of thesample pixel with respect to the optical axis of the virtual camera isadded to the direction of the optical axis of the camera itself. In thiscase, the orientation of the virtual camera may be obtained togetherwith the position of the virtual camera. Again however, for certaingames the orientation of the virtual camera may be fixed or assumed, andso no additional data or calculation may be required to account for it.

In any case, a map point is effectively projected from the viewpoint ofthe virtual camera in a direction indicated by the selected image pixel,and by distance indicated by the corresponding depth data, and locatedwithin the in-game coordinate system on the map space.

Consequently, over the course of successive images, a map dataset ofmapping points (a point cloud dataset) corresponding to the firstsequence of video images is obtained.

It will be appreciated that the image data, depth data, virtual cameraposition, orientation, and field-of-view, data may be obtained directlyfrom the game whilst being run, or may be obtained from encoded dataassociated with a video recording of the game, as encoded using any ofthe techniques described herein. Hence a map dataset can be obtained bycalculating map points whilst playing the game, or during playback ofvideo according to the techniques described herein.

It will also be appreciated, as described herein below, that a mapdataset may similarly be recorded in association with a video recordingof a game, using any of the techniques described herein, so that aplayback device does not have to calculate the map points itself.

As described above, one predetermined set of sample positions within therespective video image comprises the centreline of the image, whichtypically intersects the optical axis of the virtual camera. Howevermore generally a predetermined set of positions may comprise a samplingalong one or more horizontal lines of pixels in the image, such as forexample the centreline and positions and predetermined distances orproportions above and below the centreline or (if centreline is notused) at predetermined positions or proportions with respect to the topor bottom of the image.

Hence for example horizontal line 25% up from the bottom of the image islikely to capture the features of the terrain that may not be includedin the centreline. Meanwhile a horizontal line 75% up from the bottom ofthe image may capture relevant aerial features or other features thatmay be expected from a top-down view of a map for example, a centrelinemay intersect with the trunk of a tree, but not with the branches/canopyof a tree, which a user may expect to see in a map).

Where multiple horizontal lines are used to sample the image, theabsolute, relative or rank height of the horizontal lines may beassociated with the resulting map points. Consequently where map pointsare generated at the same position within the map space, optionally onlythe map point associated with the absolute, relative or rank highesthorizontal line may be retained. Alternatively, multiple map points atthe same position may be retained if they have different absolute,relative or rank heights.

Alternatively or in addition, one predetermined set of sample positionswithin the respective video image comprises a sampling distributionpositions over the area of the video image. Hence for example a regulararray of pixels may be sampled (for example every Nth pixelhorizontally, and every Mth pixel vertically, where N may be asdescribed previously and M may be similar). Clearly where the depthinformation is of a lower resolution than the pixel resolution, then thesampling may select pixels at an effective resolution corresponding tothat of the depth information.

In this case, a point cloud may be generated for the image frame withinthe map space, with the direction of mapping points having an elevationas well as a left/right direction relative to the optical axis of thevideogame. Consequently, a 3D representation of the map may be generatedwithin the. Such a map may still be presented in 2D if desired (i.e.ignoring elevation information), but alternatively the point cloud maybe used as the basis for rendering a 3D approximation of the mappedarea.

Alternatively or in addition, the highest elevation value in the pointcloud within a predetermined 2D area of the map may be stored inassociation with the map point to give a height value, in a similarmanner to that described above for sampling over multiple horizontallines.

Additional information that may be included in a map dataset includesthe successive positions of the virtual video camera (for example in thecase of a first-person perspective game) and/or the position of a user'savatar (for example in the case of a third-person perspective game), sothat a trace of the user's position within the map can also be recorded.

In an embodiment of the present invention, a further step comprisesobtaining colour information at the predetermined set of positionswithin the respective video image, and associating the obtained colourinformation with the corresponding generated mapping points.

In other words, points on the map may be associated with the same colouras the corresponding point within the videogame environment, enabling asubsequent graphical display of the map to resemble the videogameenvironment as if from a reduced scale top-down perspective.

To assist with this process, and referring again to FIG. 13C, it will beappreciated that not merely mapping points may be associated with, atthe corresponding point on screen, but also points along the lines ofprojection from the optical axis of the virtual camera to the mappingpoints (which as described previously herein may be calculated based onthe camera position, depth information, and direction of view from thecamera through the sample point to the virtual environment). Hence withreference to FIG. 13C, whilst the map points represent the points oftermination of lines having links corresponding to the depth informationon the image, and directions corresponding to the relative position ofthe sample pixel on screen and the virtual camera optical axis, asdescribed above, the lines emanating from the virtual camera position1420, it will be appreciated that colour information for points alongthose lines will also be available because they each represent a clearline of sight between the camera and the termination point, and colourinformation for the corresponding position of any displayed surfacebeneath those lines can be sampled for each corresponding positionwithin the map (for example per map-pixel, or every P map-pixels, whereP may be 1, 2, 3, . . . 10 etc).

In this way, the colour of unobscured the terrain visible at the currentvirtual camera position may be sampled and used to colour the map.

It will also be appreciated that use of a horizontal line place of asuitable position below the centreline of the image, and/or the use of asample distribution over the area of the image, or more generallysampling lines of sight that are not parallel to the angle of thevirtual terrain but instead converge with it at some point, will resultin lines of sight terminating on the ground/terrain of the virtualenvironment. Therefore, in the circumstances capturing colourinformation at the point of termination alone can be sufficient topopulate the map with colour information relating to the terrain, aswell as potentially elevated features such as buildings, trees etc.

It will be appreciated therefore that the map may comprise multipletypes of data, including mapping points data indicating points oftermination of lines of sight from the virtual camera taken through thepredetermined set of sample positions, and optionally simple colour datafor visible components of the terrain beneath those lines of sight,and/or similarly optionally colour data associated with the mappingpoints themselves.

As described above, the resulting stored colour information then allowsthe generation of a map or map interface that resembles the environmentseen in the game, because it effectively samples the rendered texturesof the displayed environment and stores these at corresponding positionswithin the map data.

It will be appreciated that whilst this information may be used by avideogame itself to generate a map that reflects the user's individualand potentially unique journey within the game for display duringgameplay, potentially the mapping points, and more generally a mapdataset comprising such mapping points and optionally any colourinformation as described herein, may be recorded in association with arecording of the videogame images of the kind described previouslyherein.

Hence in an embodiment of the present invention, the mapping methodcomprises the steps of recording the first sequence of video imagesoutput by the videogame, using any of the techniques described herein;recording the corresponding sequence of in-game virtual camera positionsused to create the video images, using any of the techniques describedherein; recording the corresponding sequence of depth buffer values fora depth buffer used by the videogame whilst creating the video images,using any of the techniques described herein; and recording the mappingpoints, again using any of the techniques described herein with respectto ancillary data such as event data, camera data and the like, andassociating the sequences of in game virtual camera positions, depthbuffer values and the mapping points with the recording of the firstsequence of video images, again as described previously herein.

As described previously, one of the techniques for recording depthbuffer values comprises generating a second sequence of video imagesencoding the depth buffer value sequence. As described previously, thesecond sequence of video images can accommodate corresponding ancillarydata such as virtual video camera information including a position andoptionally orientation, event data, and/or, it will be appreciated,mapping points, mapping point elevation information, mapping pointcolour information (and/or simply map colour information) and the like.

However it will be appreciated that any of the previously describedtechniques, such as use of a separate data file associated with therecording of the first sequence of video images, may be used instead.

It will also be appreciated that a map dataset comprising mappingpoints, and optionally mapping point elevation information, mappingpoint colour information and/or simply map colour information may begenerated during a single instance of play (e.g. in direct associationwith a video sequence corresponding to that instance of play), but mayalternatively or in addition be stored either locally with theentertainment device, or remotely at a server, so that successiveinstances of play may add to the this map dataset, creating a cumulativerecord of the user's exploration of the virtual environment that extendsbeyond a single instance of play.

It is possible to combine mappings obtained from individual instances ofplay because they share a common in game coordinate system.

It will be appreciated this is also true whether the individualinstances of play come from the same user, or from the sameentertainment device. Hence in an embodiment of the present invention,map datasets from multiple users may be combined, optionally withmapping points or more generally map data points other than null orunpopulated points being associated with a given user, so that multiplemaps that may occasionally cross or overlap can be disambiguated byuser.

In this way for example a user may compare his or her map with those oftheir friends, and see where different friends had shared or uniqueexperiences.

Similarly in this way an entertainment device or server may compile amore complete map of an environment that may otherwise not be easy tomap, for example if the environment is procedurally generated, byaggregating map datasets generated by a plurality of explorers of thatenvironment.

Hence the mapping method may comprise obtaining one or more additionalmap datasets generated using a sequence of video images, virtual camerapositions and depth buffer values originating from a separate instanceof the same videogame. In this case, ‘separate instance’ may equallymean a separate instance of playing the videogame on the same device bythe same user, a separate instance of playing the videogame on the samedevice by a different user, or a separate instance of playing thevideogame on a different device (by any user). Clearly ‘the videogame’itself may be a different installation of the same videogame title, whenplayed on different devices.

It is then possible to generate a graphical representation of some orall of the mapping points of at least a first map dataset, for examplefor output by the videogame.

The description above discusses the creation of the map dataset and moregenerally the mapping data points used by the map dataset using images,depth information, camera information and optionally other informationsuch as colour information obtained directly from the videogame itself.However it will be appreciated that, as described herein, video imagesfrom the game, together with depth information, camera information andoptionally other information can be recorded for subsequent playbackindependent of the source videogame itself, using one of a number oftechniques as described herein.

Consequently, it will be understood that the steps of obtaining a firstsequence of video images output by a videogame title (s1310), obtaininga corresponding sequence of in-game virtual camera positions at whichthe video images were created (s1320), and obtaining a correspondingsequence of depth buffer values for a depth buffer used by the videogamewhilst creating the video images (s1330) can all be achieved byretrieving this information from a video recording of the video gameimages and associated files (such as a second video recording encodingdepth information and other ancillary data, as described herein).

Consequently the sequence of video images can be obtained from a firstvideo recording with which the corresponding virtual camera positionsand sequence of depth buffer values are associated. Typically but notnecessarily, as described herein, the corresponding sequence of depthbuffer values is obtained from a second video recording that wasgenerated by encoding the sequence of depth buffer values.

Hence it is possible for a playback device using this recordedinformation to similarly obtain mapping points using this data, and toconstruct an equivalent map dataset, by calculating them from the image,depth, and camera data as described previously herein. The playbackdevice can then augment replay of the recorded information with mapdata, or present it separately.

Alternatively or in addition, also as described previously herein, anentertainment device may record a mapping dataset, comprising mappingpoints and optionally elevation data, colour data and the like asdescribed previously; or more generally may simply record mappingpoints, as ancillary data similar to event data or camera data, usingany suitable technique described herein, so that the data is associatedeither with the first video recording comprising the sequence of videoimages, or optionally a second video recording comprising the sequenceof depth buffer values, typically by being encoded within one of thesevideos.

In this way, advantageously the mapping points or map datasets can beincluded in such a manner that the playback device can access mappingpoints, and optionally elevation data, colour data etc., for at leastpart of the map corresponding to image data that has not yet beendisplayed (i.e. as well as map information corresponding to the currentposition being shown in the video, access map information that wouldotherwise need image/depth/camera information for positons ahead of—orbehind—that current position).

Consequently are played device can generate at least part of a mapcomprising a graphical representation of some or all of the mappingpoints of at least a first map dataset for display with the first videorecording, with parts of the map potentially corresponding to scenes notyet displayed in the video.

By displaying some or all of a map that in effect summarises the scenesin the video recording, it becomes possible to use that map as a userinterface for control of the video recording.

For example, in a video recording of a journey from a start point A toan end point B, the map will resemble a path following the cameraposition shown to the user during that journey.

Consequently, by use of a suitable user interface such as a mousepointer, slider or reticule controlled by a joystick, a position on thedisplayed map can be selected. And this meant position can act as aproxy for a desired position within the video playback.

As a result it is possible to control a playback position of the firstvideo recording by selecting a video frame whose corresponding cameraposition is closest to the selected position on the displayed map.

In this way, for example, a user can download a video of the journeyfrom a start point A to an end point B, and be presented with a mapsummarising the journey (either as an initial interface, or as anoverlay optionally superposed or placed alongside the video playback);the user can then click on points in the map and playback will jump tothe corresponding part of the video recording.

Similarly, the current camera position associated with a given displayedvideo frame can be shown on the map, so that a viewer of the video caneasily relate what they are seeing to a location on the map. This canalso assist the user to navigate through playback of the video, forexample if more conventional fast forward or rewind controls are usedinstead of or as well as directly interacting with the map.

As was discussed previously, map dataset from multiple instances ofgameplay can be combined. Accordingly, whilst playback of the currentvideo may use map data associated with that video, map datasets fromother instances of gameplay can also be accessed (for example from acentral server). Typical map datasets to access may be won by the sameuser, but with a different score or other measurable achievement, orthose of friends of the player in the current video who also play thegame, or friends of the viewer of the current video who also play thegame, or of other players identified as being of likely interest to theviewer, such as a player at the top of a local, regional, or globalleaderboard for the game, or a player who has event data within theirrecordings that is different to event data within the current videorecording (for example, in a race presently displayed video does nothave an associated crash event near the current displayed position, butanother video does have an associated crash event near the currentdisplayed position).

A graphical display of at least part of a map for a map dataset from oneor more of these additional players or play instances may be readilyincluded in conjunction with the map for the current video, because themapping points share the same in-game coordinate system.

Hence the mapping method may comprise the steps of generating a at leastpart of a first map comprising a graphical representation of some or allof the mapping points of at least a first map dataset for display withthe first video recording, and generating a at least part of a secondmap comprising a graphical representation of some or all of the mappingpoints of at least a second map dataset associated with a differentvideo recording of a different sequence of video images output by thesame videogame title and sharing the same in-game co-ordinate system,displaying at least part of the first map during playback of the firstvideo recording, the displayed part encompassing at least the currentvirtual camera position associated with the displayed video image, anddisplaying at least part of the second map during playback of the firstvideo recording if the respective part of the second map is within apredetermined range of the current virtual camera position in thein-game co-ordinate system.

In this way, the viewer of a current video can see separate maps (e.g.different meandering tracks corresponding to player movement indifferent videos) appear when gameplay depicted in another availablevideo occurs in the same or similar areas of the virtual gameenvironment to those of the current video.

Subsequently, in an embodiment of the present invention, the playbackdevice may detect whether a user interacts with a displayed part of thesecond map, and if so, switch to playback of the corresponding secondvideo.

In this way, a viewer can navigate the virtual environment from theperspective of different players, by hopping between videos when mapscorresponding to those videos suggest that the videos show scenes fromthe virtual environment that are within a threshold proximity of eachother.

The user's interaction with the second map may be similar to theirinteraction with the first map, namely that the second video starts at aframe whose virtual camera position best corresponds to the positionselected on the second map. Alternatively or in addition, a user mayindicate a desire to switch video streams at the point of closestproximity between mapping points on the two maps, or between virtualcamera positions on the two maps. Hence for example the user mayindicate a desire to switch video streams when mapping points or camerapositions substantially intersect (i.e. as the respective players in thevideos cross paths).

This gives a viewer the freedom to browse through video recordings ofthe game environment, by hopping on to recordings of different playersat corresponding places in their respective in-game journeys.

As noted previously herein, maps and by extension video recordings maybe chosen from a broader corpus of material based on any reasonablecriteria, such as video recordings made by friends of the viewer orfriends of the original player, or video recordings made by player withthe highest rankings, or video recordings having the most ‘likes’ orother indications of viewer, approval and the like.

One possibility is for a group of players within a multiplayer on-linegame to each record their own perspective of the game, and to have thesevideos associated as a group. Subsequently, using the techniquesdescribed herein, these videos can be viewed according to rules suitablefor generating a narrative of a group story. Hence for example in adeath match game where two players come together so that the maps oftheir two videos intersect, if one of the players kills the other, thenif a user is watching a video of the victorious player, the videocontinues, whereas if a user is watching a video of the vanquishedplayer, then the video switches to that of the victorious player at apoint where they respective camera positions of the two players is thattheir closest, optionally after the killing event. In this case, forexample, event information is also encoded to indicate the nature ofsuch interactions. In a similar manner, in a racing game the videoplayback could switch to anyone who overtakes the current leader, forexample.

As was noted previously herein, it will be appreciated that the methodsdescribed herein may be carried out on conventional hardware suitablyadapted as applicable by software instruction or by the inclusion orsubstitution of dedicated hardware. Thus the required adaptation toexisting parts of a conventional equivalent device may be implemented inthe form of a computer program product comprising processorimplementable instructions, stored or conveyed by any suitable means, asdiscussed previously.

Hence for example the hardware for an entertainment device operable toimplement the mapping techniques described herein may be a conventionalcomputing device such as a PlayStation 4 operating under suitablesoftware instruction, comprising a video data processor (such as CPU 20Aand/or GPU 20B) configured (for example by suitable softwareinstruction) to obtain a first sequence of video images output by avideogame title; a camera position data processor (such as CPU 20Aand/or GPU 20B) configured (for example by suitable softwareinstruction) to obtain a corresponding sequence of in-game virtualcamera positions at which the video images were created; a depth dataprocessor (such as CPU 20A and/or GPU 20B) configured (for example bysuitable software instruction) to obtain a corresponding sequence ofdepth buffer values for a depth buffer used by the videogame whilstcreating the video images; and a mapping data processor (such as CPU 20Aand/or GPU 20B) configured (for example by suitable softwareinstruction), for each of a plurality of video images and correspondingdepth buffer values of the obtained sequences, to obtain mapping pointscorresponding to a selected predetermined set of depth valuescorresponding to a predetermined set of positions within a respectivevideo image; wherein for each pair of depth values and video imagepositions, a mapping point has a distance from the virtual cameraposition based upon the depth value, and a position based upon therelative positions of the virtual camera and the respective video imageposition, thereby obtaining a map dataset of mapping pointscorresponding to the first sequence of video images.

It will be apparent to a person skilled in the art that variations inthe above hardware corresponding to the various techniques as describedand claimed herein are considered within the scope of the presentinvention, including but not limited to:

-   -   the predetermined set of positions comprising pixels sampled        from one or more horizontal lines across the respective image;    -   the predetermined set of positions comprising a sampling        distribution of positions over the area of the video image;    -   a colour processor (such as CPU 20A and/or GPU 20B) configured        to obtain colour information at the predetermined set of        positions within the respective video image, and associate the        colour information with the corresponding generated mapping        points;    -   hardware as described previously herein adapted to record the        first sequence of video images output by the videogame, record        the corresponding sequence of in-game virtual camera positions        used to create the video images, record the corresponding        sequence of depth buffer values for a depth buffer used by the        videogame whilst creating the video images (for example by        generating a second sequence of video images encoding the depth        buffer value sequence), and record the mapping points (and        optionally mapping colour data, elevation data and the like),        and to associate the sequences of in game virtual camera        positions, depth buffer values and the mapping points with the        recording of the first sequence of video images;    -   a map processor (such as CPU 20A and/or GPU 20B operating under        suitable software instruction) configured to obtain one or more        additional map datasets generated using a sequence of video        images, virtual camera positions and depth buffer values        originating from a separate instance of the same videogame;    -   a graphical output processor (such as CPU 20A and/or GPU 20B        operating under suitable software instruction) configured to        generate a graphical representation of some or all of the        mapping points of at least a first map dataset, for output by        the videogame;    -   the sequence of video images being obtained from a first video        recording, with which the corresponding virtual camera positions        and sequence of depth buffer values are associated;    -   the corresponding sequence of depth buffer values being obtained        from a second video recording that was generated by encoding the        sequence of depth buffer values;    -   the mapping points being obtained from data associated with a        first video recording comprising the sequence of video images,        or a second video recording comprising the sequence of depth        buffer values;    -   a map interface processor (such as CPU 20A and/or GPU 20B        operating under suitable software instruction) configured to        generate a at least part of a map comprising a graphical        representation of some or all of the mapping points of at least        a first map dataset for display with the first video recording,        select a position on the displayed map using a user interface,        and control a playback position of the first video recording by        selecting a video frame whose corresponding camera position is        closest to the selected position on the displayed map;    -   a map interface processor (such as CPU 20A and/or GPU 20B        operating under suitable software instruction) configured to        generate a at least part of a first map comprising a graphical        representation of some or all of the mapping points of at least        a first map dataset for display with the first video recording,        generate a at least part of a second map comprising a graphical        representation of some or all of the mapping points of at least        a second map dataset associated with a different video recording        of a different sequence of video images output by the same        videogame title and sharing the same in-game co-ordinate system,        display at least part of the first map during playback of the        first video recording, the displayed part encompassing at least        the current virtual camera position associated with the        displayed video image, and display at least part of the second        map during playback of the first video recording if the        respective part of the second map is within a predetermined        range of the current virtual camera position in the in-game        co-ordinate system; and        -   the map interface processor being configured to detect            whether a user interacts with a displayed part of the second            map, and if so, switch to playback of the corresponding            second video.

3D Mapping

Building on the above principles, it is also possible to generate a 3Dmap (e.g. comprising elevation data to form at least a partialreconstruction of the mapped environment) from the gameplay of one ormore users.

As discussed previously, a game typically generates an image (RGB)buffer at the game resolution; typically 1280×720 pixels, or 1920×1080pixels, or any other common resolution format. The colour informationper pixel may in turn be 24 bits (8 bits per colour channel), forexample. The game typically also generates a depth buffer, typically atthe same resolution as the image buffer (though optionally at a lowerresolution, and relying on interpolation). The depth data per ‘pixel’may for example be 16 bits, as discussed previously.

In addition, for each image frame, the virtual camera position andorientation may be captured, and optionally also the field of view ifthis is variable (for example when using an in-game sniper scope, orexperiencing an in-game health effect that limits vision).

Optionally also events and in-game entities may be recorded as discussedpreviously. Information for recorded entities (such as non-playercharacters, or opponents) may include their position, orientation, type,group/class (e.g. team A or B, the player or an NPC), and/or an instanceidentifier. Optionally this information may be used to identify where atemporary/transitional object is captured in the image, so that it canbe subsequently removed from the mapping process.

As was described previously herein in relation to the 2D map, a set oftransformations transcribe 3D points within the game world to 2D pointswithin the captured image, according to a standard pipeline for suchgames. These typically include transforming co-ordinates of elements inthe game environment through a camera matrix (or ‘view matrix’), andtypically also through a perspective projection matrix (or ‘clipmatrix’). Other transforms may also be performed, for example placinglocal model co-ordinates within a world co-ordinate system as apreparatory step.

Consequently, referring to the previously described techniques formapping a virtual environment, the steps comprise obtaining a firstsequence of video images output by a videogame title, obtaining acorresponding sequence of in-game virtual camera positions at which thevideo images were created, obtaining a corresponding sequence of depthbuffer values for a depth buffer used by the videogame whilst creatingthe video images, and for each of a plurality of video images andcorresponding depth buffer values of the obtained sequences, obtainmapping points corresponding to a sampling distribution of points overthe area of a respective video image and their associated depth values;wherein respective mapping points are obtained by projectingco-ordinated derived from the sample points from the video image andassociated depth values back into a 3D game world co-ordinate system ofthe videogame title; thereby obtaining a point cloud dataset of mappingpoints corresponding to the first sequence of video images.

In this case, a sampling distribution of positions over the area of thevideo image corresponds to the predetermined set of positions within arespective video image. The sampling may be 1:1 (i.e. all pixels of thevideo image) or a sub-sampling, such as 1:2 (i.e. a chequerboard) or 1:4(e.g. one pixel per 2×2 block of pixels). Conversely pixels may beinterpolated to increase effective resolution (super-sampling). Othersampling distributions may be similarly considered, such as a randomsample distribution, or a Gaussian sample distribution centred on theimage centre.

Hence referring now to FIG. 14 , the 3D mapping technique can be seen asa variant on the method of FIG. 12 , and comprises:

-   -   in a first step s1510, obtaining a first sequence of video        images output by a videogame title;    -   In a second step s1520, obtaining a corresponding sequence of        in-game virtual camera positions at which the video images were        created;    -   In a third step s1530, obtaining a corresponding sequence of        depth buffer values for a depth buffer used by the videogame        whilst creating the video images;

Then in a fourth step s1540, for each of a plurality of video images andcorresponding depth buffer values of the obtained sequences,

-   -   a sub-step s1542 of obtaining mapping points corresponding to a        sampling distribution of points over the area of a respective        video image and their associated depth values.    -   As noted above, these are obtained in a further sub-step s1544        by projecting co-ordinates derived from the sample points from        the video image and associated depth values back into a 3D game        world co-ordinate system of the videogame title, thereby        obtaining a point cloud dataset of mapping points corresponding        to the first sequence of video images.

In an embodiment of the present invention, in relation to sub-step s1544then given the set of points and the depth information (sampled,sub-sampled or interpolated as appropriate) the 3D-to-2D transforms usedto create the output image can be reversed to reconstruct the 3D points,for example in the game world co-ordinate system. Hence an inverseperspective projection matrix may be applied, followed by an inversecamera matrix, to arrive at a set of data points within the worldco-ordinate system. Hence projecting sample points from the video imageback into a 3D game world co-ordinate system may comprise transformingco-ordinates output by an inverse perspective projection matrix throughan inverse camera matrix. Similarly, projecting sample points from thevideo image back into a 3D game world co-ordinate system may comprisetransforming co-ordinates output by an inverse perspective projectionmatrix through an inverse camera matrix.

Alternatively or in addition, in relation to sub-step s1544, then withreference to FIG. 15 then in an embodiment of the present invention isit appreciated that the view in the image fills a view frustum in thegame world, resembling an expanding wedge of space. As a result, allpoints in the image can be thought to lie on lines of projection withinthis frustrum.

Accordingly, 3D points can be generated very quickly by interpolating aposition between a near-image plane and a far-image plane (defining thefrustum) using the associated depth values. The values of ‘near’ and‘far’ may be predetermined. Typically the near and far image planes areset to encompass the full range of depth values and so are located atpositions corresponding to a depth value of ‘1’ and ‘65535’ (for a 16bit depth). Alternatively, the near and far image planes may be set atpositions corresponding to the closest and furthest actual depth valueswithin a given depth image.

Optionally, the inverse projection techniques described above may beused to project the near and/or far image planes for this purpose.

In other words, the x,y,z position of a point sampled from the imagewill be at a position along a line between that sample point position inthe near image plane, and the sample point position in the far imageplane, the position along the line being proportional to the depth dataassociated with that sample point.

Optionally, this process of frustum point gathering may initially assumethe virtual camera is at the game world origin, and then transpose theresulting 3D points within the world co-ordinate system according to thevirtual camera position/orientation information.

Hence using either technique, the sample points of the 2D video imageoutput by a videogame are projected back into the 3D game worldco-ordinate system (e.g. a co-ordinate system consistent with the 3Dgame world co-ordinate system within the game, and within which a map ofthe game world can be assembled) to create mapping points. The origin,scale or other aspects of the co-ordinate system are not essential,providing the projection into that co-ordinate system is performedconsistently, but clearly it is preferable to have a 1:1 correlationbetween the in-game world co-ordinate system and the generated map.

The result is a 3D point cloud representation of the game environment asseen in the video image.

Over successive images in a video sequence, additional sets of mappingpoints are created, adding to the 3D point cloud representation of thegame environment within the game world co-ordinate system, to form apoint cloud dataset of mapping points.

In this way, a point cloud representation of the parts of the gameenvironment seen by the user during play is built up through analysis ofsuccessive output video images.

Optionally, points in the 3D point cloud can be snapped to a notionalgrid (i.e. a 3D or volumetric grid). The resolution of this grid (i.e.the pitch size) may be equal to a cube having sides the size of a singlepixel within the game environment at the near image plane used whenfrustum point gathering, or conversely the far image plane, representinga unit volume of the grid. This may be useful for example where thecalculated position of a point using either of the 2D to 3D projectiontechniques described above results in a point having a very preciselocation value that in effect occupies an arbitrary position within aunit volume of the notional grid. Hence the potential change of positionof a given point may be in this case small, but serves to regularisepoint positions and, as explained below, simplify the identification ofsubsequent co-located points.

Alternatively the grid may have a unit volume of a size comparable tothe scale of the environment within the game world. Hence the grid mayequate for example to a 1×1 cm cube or a 10×10 cm cube for gameenvironments with a lot of detail, for example indoors, or a 1×1 m cubeor a 10×10 m cube for large environments, or a 100×100 m cube 1 km×1 kmcube or more, for example for a space-based game surveying planets.

Optionally, by virtue of the common game world coordinate system used todefine the position of a 3D point, point clouds derived from outputvideo images of multiple game instances (either by the same user oversuccessive plays, and/or from multiple users) may be combined to form amore complete point cloud representation of the game environment.

Merging point clouds from successive video images within the sequence ofvideo images output by a videogame title, typically within a singlegaming session, but optionally within successive sessions of the userand/or sessions from several users, can benefit from some datasanitisation.

As noted above, snapping the projected points to a 3D grid makes itsimpler to compare co-located points originating from different imageframes.

Co-located points can be culled down to 1 point in a grid unit, and/orpoints can be combined using an appropriate data format (kd-tree, octreeor the like).

Points that only appear in than a predetermined number of contiguousimage frames or fewer may be culled; these can be assumed to representmoving entities whose position changes during the course the game, andso do not necessarily represent the feature of the map environment. Thepredetermined number may be anything from one up to the number of framesgenerated in a second, two seconds, or more, or may be a variable valuebased upon the relative velocity of the virtual camera (with a smallernumber when the camera is fast, and a larger number when the camera slowor stationary, where fast and slow may be classified by a predeterminedthreshold value).

Alternatively or in addition, areas surrounding the known location of anentity such as an NPC may be more aggressively culled, where suchlocations have been captured.

Finally, normals may be generated from the depth data (depth buffervalues). For example, for a given depth pixel (i.e. a depth valuecorresponding to a given image pixel), the surrounding depth values areused to create two vectors. The depth pixels above and below the currentpixel form vector 1. The depth pixels to the left and to the right ofthe current pixel form vector 2. The cross product of these two vectorsis an approximation to the normal. Optionally, passing the depth bufferthrough a bilateral filter first produces a better approximation of thenormal.

Given the 3D point cloud derived from one or more sequences of videoimages output by the videogame title, a surface (e.g. a mesh) can bereconstructed for the game environment represented by the point cloud,using any suitable technique for generating a surface from a 3D pointcloud, and in particular one that may have variable density andcoverage.

Example techniques known in the art include a screened Poisson surfacereconstruction based on the point cloud, and ball-pivot surfacereconstruction based on the point cloud.

For the screened Poisson surface reconstruction, clipping of theresulting surface to a region within a predetermined distance of pointswithin the point cloud may be used to limit the resulting surface to theknown area of the game environment captured by the point cloud dataset.

As was noted previously herein, it will be appreciated that the methodsdescribed herein may be carried out on conventional hardware suitablyadapted as applicable by software instruction or by the inclusion orsubstitution of dedicated hardware. Thus the required adaptation toexisting parts of a conventional equivalent device may be implemented inthe form of a computer program product comprising processorimplementable instructions, stored or conveyed by any suitable means, asdiscussed previously.

Hence for example the hardware for an entertainment device operable toimplement the mapping techniques described herein may be a conventionalcomputing device such as a PlayStation 4 operating under suitablesoftware instruction, comprising a video data processor (such as CPU 20Aand/or GPU 20B) configured (for example by suitable softwareinstruction) to obtain a first sequence of video images output by avideogame title; a camera position data processor (such as CPU 20Aand/or GPU 20B) configured (for example by suitable softwareinstruction) to obtain a corresponding sequence of in-game virtualcamera positions at which the video images were created; a depth dataprocessor (such as CPU 20A and/or GPU 20B) configured (for example bysuitable software instruction) to obtain a corresponding sequence ofdepth buffer values for a depth buffer used by the videogame whilstcreating the video images; and a mapping data processor (such as CPU 20Aand/or GPU 20B) configured (for example by suitable softwareinstruction), for each of a plurality of video images and correspondingdepth buffer values of the obtained sequences, to obtain mapping pointscorresponding to a sampling distribution of points over the area of arespective video image and their associated depth values, whereinrespective mapping points are obtained by projecting co-ordinatesderived from the sample points from the video image and associated depthvalues back into a 3D game world co-ordinate system of the videogametitle, thereby obtaining a point cloud dataset of mapping pointscorresponding to the first sequence of video images.

Combining 3D Mapping and Video Playback

In embodiments of the present invention a recorded or streamed videoshowing gameplay of a respective player during a game session iscombined with a 3D map of the type described previously herein.

In principle, in this case the video only requires an associateddescription of the viewpoint of the first camera (i.e. the camera usedwhen capturing video frames as described previously herein), but doesnot require other supplementary data such as depth data or event data(although either might be available). In particular the depth data isnot needed, since the 3D map has already been formed.

The video is then displayed at a positon on the 3D map that correspondswith the position of the first camera when capturing the currentlydisplayed video frame, optionally with any suitable offset along theoptical axis of that first camera to account for a different playbackviewpoint, as described later herein. Typically the video is rendered asa texture that is applied to a flat surface inserted into thereconstructed environment of the 3D map at the appropriate position.

As a result, the video can be thought of as a 2D video sequence thatroams around the 3D map as it is played back, based on the changingposition and orientation of the first camera with respect to the 3D mapover the course of the footage within the video.

In addition, during playback a virtual second camera views the 3D mapcomprising this video sequence in order to provide a final view to auser.

Optionally the second camera can coincide with the position andorientation of the recorded camera position, so that the final viewcoincides with just the 2D video sequence. As will be appreciated fromFIG. 15 , the camera position and the actual position of an image planemay not be coincident, but may have a predetermined offset. If therelationship between the first camera and the 2D video and the secondcamera and the 2D video is different, then a corrective offset along theoptical axis of the first camera can be used by the second camera sothat the image plane of the 2D video coincides with the image plane ofthe second camera, so that the 2D video sequence properly and fullyoccupies the second camera image.

However, in response to a user input via a UI, and/or in response to apredetermined condition (or, where included as supplementary data, inresponse to a predetermined event indicated by event data), then thesecond camera can change position.

In one instance, referring now to FIG. 16 , the second camera can pullback parallel to the optical axis of the first camera, so that thesecond camera captures a view of both the 2D video 1610 and some or allof the 3D map 1620.

In this way, the limited viewpoint of the original 2D image is expandedby the apparent integration of the video into a wider representation ofthe reconstructed 3D environment, with the viewpoint within thatreconstructed 3D environment being updated responsive to the viewpointof the 2D video so that this apparent integration remains consistent asthe viewpoint of the 2D video changes.

It will be appreciated that optionally the user may be free to lookaround within the reconstructed 3D environment of the map, for exampleto look to the left, right above, below or behind the position of thesecond camera, which acts as their own viewpoint. The user may also befee to move the second camera position in order to navigate the 3D mapindependently of the video. In these cases, however, a UI such as abutton or menu item may allow the user to re-centre upon and track thevideo again. Meanwhile optionally the video may fade out to transparencyand/or no longer be displayed if the user navigates beyond a certainrange from the video, and/or beyond a certain angle away from theoptical axis of the first camera.

Optionally further, data regarding other dynamic elements of the game(e.g. elements that may not be part of the reconstructed 3D environment,such as other players or in-game non-player characters) may be includedas supplementary data with the video in the manner described previouslyherein, or in the case of a live stream, may optionally be received inparallel via another link within a network.

An indicator object representing of one or more dynamic elements and/orany other notable feature of the environment, (such as a finish line,health pack, or an event corresponding to associated event data, asapplicable) can then be included within the reconstructed 3D environmentto provide an idea of where they are with respect to the videoviewpoint. This can provide the user/viewer with the ability toanticipate when an encounter with a dynamic element will occur, or trackthe progress of a dynamic element beyond the field of view of the 2Dvideo.

FIG. 17 provides an example of a view comprising a 1710 video,reconstructed 3D environment 1720 and an indicator object 1730 for adynamic element (another player's car, and a trail of its position)within the game Overload®.

Optionally different representations/indicator objects can be used fordifferent dynamic elements or other features, for example based on type.Such representations can be generic or tailored to the specificvideogame to which the video relates.

In an embodiment of the present invention, the above techniques could beprovided for a plurality of players within a single game session, sothat a viewer could switch between recorded or streamed videos ofdifferent players, as well as viewing the wider reconstructedenvironment that those players are sharing by zooming out from the videoviewpoint and/or turning/moving in a different direction, as describedpreviously herein. Indeed, as a mechanism for switching playerviewpoints, a system could automatically navigate through the 3D mapbetween the viewpoints of respective first cameras of different playersso that a viewer can appreciate their relative positions within theenvironment.

Such approaches would allow viewers/spectators to see more than any onegiven player can, and to get an overall view of what was (or indeed is,in the case of a live-event) happening at particular times in the game.

It will be appreciated that in such a case, the plurality of videostreams need to be identified as being part of the same in-game session.This may be done by a unique game-session identifier, associated witheach video or stream created during that session. This may optionally beincluded within a title of each recording or stream to enable a systemto search for linked videos within a legacy hosting service such asYouTube® or Twitch®. Alternatively or in addition, each video or streammay optionally contain identifier pointing to at least one of the othervideos or streams on a network (such as the internet), so that access toone stream enables eventual access to any of the others. Finallyalternatively or in addition, separate information about a video/stream,including whether it is part of a group, may optionally be accessed froman administrative server. For example, an identifier or link similar tothose noted above may instead be sent to and parsed by a server, whichholds associative records indicating which, if any, other videos/streamscorrespond to the same game session.

It will be appreciated that, whilst as noted above the videos usedwithin the 3D map do not need associated depth data, in principle a 3Dmap could be generated at the same time as one or more videos are hostedwithin it using such depth data and the techniques described herein,provided that the map and the videos/depth data all share a commonreference. In this way a viewer could watch with the players as theyexplore and reveal a new map.

Hence whilst for many uses, such as e-sports coverage, it would bepreferable to have already built a detailed reconstruction of the gameenvironment, optionally the construction of a map as part of thedocumentary process of viewing a game session may be valuable for gameswhere the environment is procedurally generated and is unique to thatgame session, or thanks to procedural generation is so large that it isnot feasible to anticipate where the players will go, such as forexample in a game like No Man's Sky®.

It will be appreciated that in such a case for pre-recorded videos, themost complete reconstruction of the environment would be achieved at theend of all the videos, and this could then be used from the start of anysubsequent playback. Meanwhile for a live stream, the map would growmore complete as the stream went on.

It will be appreciated that an advantage of embedding videos within a 3Dmap/reconstruction of the wider environment shown within the videogameis that a system can control how that wider environment is displayed,potentially to enhance the enjoyment or understanding of the viewer.

For example, the map can be displayed top-down or from an elevatedvantage point, and/or as a blue-print (see FIG. 18B), or some or all ofthe environment can be rendered transparent or partially transparent(see FIG. 18C) so viewers can see action within interiors of buildings,caves, tunnels, etc. Where an indictor object representing a dynamicelement such as a player or NPC is to be provided in conjunction with atransparent or semi-transparent rendering of the map, it may bedisplayed differently according to whether it is inside or outside astructure, or similarly whether it is occluded by a now-transparentfeature of the environment. For example a representation of the dynamicelement may be blurred and/or desaturated, or replaced with a glow. Anysuitable change, typically consistent with the relevant game, may beconsidered by a designer. Optionally, one or more of a player, streamer,recorder, broadcaster, server administrator, or the viewer can selecthow they wish to the reconstruction, and optionally representations ofdynamic elements, to be displayed.

As noted above it is be preferable to have already built a detailedreconstruction of the game environment, for example using the techniquesdescribed previously herein. However, it will be appreciated that theremay be parts of an in-game environment that a player never looks at andhence never provides mapping information for, but which aviewer/spectator might do. An example may be a bridge or other structurein a racing game; players will tend to concentrate on what is ahead ofthem, and are unlikely to look back and hence provide image data aboutthe opposite sides of structures in such a game.

To address this, a video (and associated depth data) may be recordedthat deliberately explores such non-player views. This may be donewithin the normal operations of a game, for example by deliberatelydriving in the wrong direction on a race track to capture acomplementary view of game assets. Alternatively or in addition it maybe done by using a virtual ‘drone’, which may be provided by a game'sdeveloper, which can move freely within the game environment. A similareffect may be achieved by use of a cheat code or developer code toaccess modes such as so-called ‘God mode’ or ‘no clip’, which similarlyallow free movement of the first camera, compared to normal gameplay. Adrone or untethered virtual camera could be controlled by a user, orcould follow a scripted or heuristically driven path to cover apredetermined distribution of positions within the game environment.

The 3D map may then be made using this video and depth data, or with theadditional contribution of such information.

Notably, the present invention does not require access to game code, butinstead relies upon a virtual camera and position and depth data togenerate the 3D map, and a virtual camera and position data tosubsequently embed one or more camera views within that 3D map.

Hence in principle the present invention can also be applied to mappingand showing real-world environments; for example, a formula 1 racetrack. If either a stereoscopic camera or a camera and depth mappingsensor were used on the track, together with GPS and/or other positiontracking technologies, then a 3D map reconstructing the track could begenerated from the combination of video, position and depth data (eitherobtained from the depth mapping sensor or from processing thestereoscopic images).

Subsequently conventional video feeds from one or more cars during arace, together with camera position data derived from GPS and/or otherposition tracking technologies, could be embedded within the 3D map inthe manner described previously herein, and typically a broadcaster orviewer could change viewpoints, navigate the track, switch betweendrivers and the like as described herein previously for a virtualenvironment.

Such an approach could be used for any sport or event where the venuehas been reconstructed in 3D (or could be reconstructed during a livestream as described previously herein) and for which videos withassociated position tracking could be captured by one or moreparticipants in the sport or event.

The above approach may be implemented by suitable software instructionusing hardware such as the PS4® entertainment system (10) of FIG. 1 ,but in principle could be implemented by suitable software acting as aplug-in or other executable code within a browser.

To assist with managing the potential size of the 3D map reconstructionin a browser, the underlying data can be simplified to enable handlingby the browser, and timely transmission to the browser.

The point cloud of the map can be broken up onto blocks manageable bythe browser clients, and converted into triangles (polygons) for exampleusing screened Poisson reconstruction. The resulting meshes can befurther reduced in size using quadric mesh simplification. Then colourdata from the nearest points within the relevant block of the pointcloud can be used to paint the reduced mesh.

Data files can then be downloaded to the browser as polygon mesh chunks.Chunks for portions of the map not currently available can be downloadedwhen the second camera points toward such a portion, for exampledownloading chunks at a suitable draw distance from the current secondcamera position.

Optionally, a further reduced polygon mesh of a larger portion of themap (or the full the map) may be used when a chunk is not yet available,thereby providing a lower level of detail reconstruction if there aredelays accessing a more detailed mesh.

The browser can synchronise received video with the 3D map on a frame byframe basis using the associated first camera position data, aspreviously described, and render the 3D map scene with the embeddedvideo texture. The browser can switch between videos or streams in thosecases where a user wants to change viewpoint between multiple players,by used of corresponding timestamps, frame counters or the like.

It will be appreciated that an application dedicated to the combinedvideo and map technique may operate similarly, but may have access toprocessing and memory resources that mean mesh simplification is notrequired (or to a lesser extent) and/or that the mesh can be held inmemory in its entirety (or in larger chunks).

Variants of Combined Map and Playback

Different first cameras may have different properties, such as differentfields of view, and these can be associated with a video assupplementary data and used where necessary to modify the properties orpositional offsets of the second camera.

One or more first cameras may be provided that do not correspond toplayers or participants within a game but may correspond to an NPC(thereby giving the NPC's perspective). Similarly, referring now also toFIG. 18A, one or more first cameras may provide an overview of all orpart of the reconstructed environment from a high and/or distant vantagepoint; this could provide a summary view of the session that is faithfulto what is displayed (e.g. all players are shown as they are renderedin-game), but a used could then navigate ‘though’ this vantage point anddown into the 3D map to join the viewpoint of a participant, or simplyinspect the mapped environment more closely. In a live stream of anevent, this camera may be under the control of the broadcaster toprovide relevant overviews of the action. As noted previously this couldbe done using a drone or developer feature such as no-clip or god-mode.

In addition to embedding a video image within the 3D map, indicatorobjects (such as for dynamic elements) may be rendered; optionally, someof these may be provided on top of the video image (e.g. in front of theimage from the viewpoint of the second camera, despite being behind thevideo image on the map from that same viewpoint).

FIG. 19A shows a render of the 3D map together with dynamic objects (atriangular wedge indicating the position and direction of the playerassociated with the first camera, and a series of columns 1930indicating the locations of key items).

FIG. 19B shows the integration of the video image, with the renderedvehicle of the player replacing the wedge, but the columns 1930 beingrendered last (with respect to the 3D model and video) to provide anintegrated overlay that appears consistent with the video image.

Referring now to FIG. 20 , in a summary embodiment of the presentinvention, a method of video playback comprises:

-   -   in a first step s2010, obtaining a 3D reconstruction of at least        part of an environment;    -   in a second step s2020, obtaining video footage of an activity        within that at least part of the environment;    -   in a third step s2030, obtaining data indicating a position and        orientation of a first camera within the at least part of the        environment that recorded the obtained video footage; and    -   in a fourth step s2010, rendering a view of the video footage in        alignment with a corresponding view of at least part of the 3D        reconstruction, responsive to the position and orientation of        the first camera within the at least part of the environment.

It will be apparent to a person skilled in the art that variations inthe above method corresponding to operation of the various embodimentsof the apparatus as described and claimed herein are considered withinthe scope of the present invention, including but not limited to:

-   -   the environment and the first camera being either real or        virtual as described previously herein;    -   rendering at the viewpoint of a second, virtual camera        positioned at a predetermined offset along the optical axis of        the first camera, as described previously herein;    -   altering the rendering viewpoint of a second camera in response        to an input from a user, as described previously herein;    -   returning the rendering viewpoint of a second, virtual camera        from its current position to a position having a predetermined        offset along the optical axis of a first camera as described        previously herein (for example either for the previously viewed        first camera so as to return to existing footage, or the first        camera associated with a switched video feed so as to navigate        across the map to the in-map position of the new footage);    -   a first camera being one selected from the list consisting of a        virtual camera coincident with the viewpoint of a player within        a virtual environment, a virtual camera coincident with the        viewpoint of a non-player character within a virtual        environment, and a virtual camera positioned independently of        any player or non-player character within a virtual environment,        at a raised vantage point (for example as a virtual drone used        for this purpose, or equivalently using a god-mode or no-clip        mode viewpoint, which if applied to a player viewpoint can be        understood to take the player out of conventional play and        convert them into such a drone);    -   multiple instances of video footage and associated camera        position and orientation data being available (for example        corresponding to a plurality of players in a multiplayer game,        or one or more players and one or more NPCs), and obtaining        second video footage of an activity within that at least part of        the environment, together with data indicating the associated        camera position and orientation within the at least part of the        environment, switching to the second video footage; and in which        the rendering step comprises switching to render a view of the        second video footage in alignment with a corresponding view of        at least part of the 3D reconstruction, responsive to the        associated camera position and orientation within the at least        part of the environment;    -   the 3D reconstruction of at least part of virtual environment        being obtained from images, depth data and camera position data        generated by a virtual camera that does not correspond to an        in-game participant and is free to move in three dimensions (for        example using a drone or free navigation mode as described        previously, optionally in conjunction with the data-supplemented        recording or streaming techniques described previously herein);    -   the 3D reconstruction of at least part of virtual environment        being obtained from images, depth data and camera position data        generated by one or more participants of a videogame (for        example using the data-supplemented recording or streaming        techniques described previously herein);    -   in these latter two cases, the 3D reconstruction comprising the        steps of obtaining a first sequence of video images output from        a videogame title, obtaining a corresponding sequence of in-game        virtual camera positions at which the video images were created,        obtaining a corresponding sequence of depth buffer values for a        depth buffer used by the videogame whilst creating the video        images, and for each of a plurality of video images and        corresponding depth buffer values of the obtained sequences,        obtaining mapping points corresponding to a sampling        distribution of points over the area of a respective video image        and their associated depth values, wherein respective mapping        points are obtained by projecting co-ordinates derived from the        sample points from the video image and associated depth values        back into a 3D game world co-ordinate system of the videogame        title, thereby obtaining a point cloud dataset of mapping points        corresponding to the first sequence of video images;    -   each of one or more obtained video footage being one or more        selected from the list consisting of previously recorded video        footage, and a live video stream;    -   video footage for a plurality of simultaneous viewpoints being        available (again for example from a plurality of players in a        multiplayer game), and obtaining a session ID associated with at        least a first one of the videos, and identifying and obtaining        at least a second one other of the videos using the session ID        (for example by searching for that ID in a legacy or dedicated        hosting service, or using the ID to directly access an indicated        source of the video footage there the ID enable this), and in        which the step of rendering a view comprises switching from the        first video to the second video, and rendering a view of the        second video footage in alignment with a corresponding view of        at least part of the 3D reconstruction, responsive to the        position and orientation of the first camera in the second video        footage within the at least part of the environment; and    -   rendering one or more representations of virtual dynamic        objects, the dynamic objects not being part of the 3D        reconstruction and being located with respect to the second        camera and the 3D reconstruction behind the video image, the        representations of virtual dynamic objects being displayed in        front of the video image, as described previously in conjunction        with FIGS. 19A and 19B.

As noted elsewhere herein, these methods may be carried out onconventional hardware suitably adapted as applicable by softwareinstruction or by the inclusion or substitution of dedicated hardware,in the form of a computer program product comprising processorimplementable instructions stored on a non-transitory machine-readablemedium, realised in hardware, or transmitted via data signals, aspreviously described.

Hence for example, an entertainment device 10 such as the SonyPlayStation 4 ®, may comprise a receiver (such as Ethernet® or Wifi®ports 32, 34, in conjunction with CPU 20A running under suitablesoftware instruction) operable to obtain a 3D reconstruction of at leastpart of an environment; a receiver (such as Ethernet® or Wifi® ports 32,34, in conjunction with CPU 20A running under suitable softwareinstruction) operable to obtain video footage of an activity within thatat least part of the environment; a receiver (such as Ethernet® or Wifi®ports 32, 34, in conjunction with CPU 20A running under suitablesoftware instruction) operable to obtain data indicating a position andorientation of a first camera within the at least part of theenvironment that recorded the obtained video footage; and a renderingprocessor (Such as GPU 20B and/or CPU 20A running under suitablesoftware instruction) operable to render a view of the video footage inalignment with a corresponding view of at least part of the 3Dreconstruction, responsive to the position and orientation of the firstcamera within the at least part of the environment.

It will also be appreciated that under suitable software instructionsuch an entertainment device will be operable to implement the othermethods and techniques described herein.

The invention claimed is:
 1. A method of video playback, comprising:obtaining a 3D reconstruction of at least part of an environment;obtaining video footage of an activity within that at least part of theenvironment; obtaining data indicating a position and orientation of afirst camera within the at least part of the environment that recordedthe obtained video footage; and rendering a view of the video footage inalignment with a corresponding view of at least part of the 3Dreconstruction, responsive to the position and orientation of the firstcamera within the at least part of the environment, wherein: the 3Dreconstruction of at least part of virtual environment is obtained fromimages, depth data and camera position data generated by at least oneof: (i) a virtual camera that does not correspond to an in-gameparticipant and is free to move in three dimensions, and (ii) one ormore participants of a videogame, and the obtaining the 3Dreconstruction of at least part of the environment includes: obtaining afirst sequence of video images output from a videogame title; obtaininga corresponding sequence of in-game virtual camera positions at whichthe video images were created; obtaining a corresponding sequence ofdepth buffer values for a depth buffer used by the videogame whilstcreating the video images; and for each of a plurality of video imagesand corresponding depth buffer values of the obtained sequences,obtaining mapping points corresponding to a sampling distribution ofpoints over the area of a respective video image and their associateddepth values; wherein respective mapping points are obtained byprojecting co-ordinates derived from the sample points from the videoimage and associated depth values back into a 3D game world co-ordinatesystem of the videogame title, thereby obtaining a point cloud datasetof mapping points corresponding to the first sequence of video images.2. The method of video playback according to claim 1, in which theenvironment and the first camera are virtual.
 3. The method according toclaim 1, in which the step of rendering comprises: rendering at theviewpoint of a second, virtual camera positioned at a predeterminedoffset along the optical axis of the first camera.
 4. The methodaccording to claim 1, comprising altering the rendering viewpoint of asecond camera in response to an input from a user.
 5. The methodaccording to claim 4, comprising returning the rendering viewpoint of asecond, virtual camera from its current position to a position having apredetermined offset along the optical axis of the first camera.
 6. Themethod according to claim 1, in which a first camera is one or more of:i. a virtual camera coincident with the viewpoint of a player within avirtual environment; ii. a virtual camera coincident with the viewpointof a non-player character within a virtual environment; and iii. avirtual camera positioned independently of any player or non-playercharacter within a virtual environment, at a raised vantage point. 7.The method according to claim 1, in which multiple instances of videofootage and associated camera position and orientation data areavailable, the method comprising: obtaining second video footage of anactivity within that at least part of the environment, together withdata indicating the associated camera position and orientation withinthe at least part of the environment; and switching to the second videofootage; and in which the rendering step comprises: switching to rendera view of the second video footage in alignment with a correspondingview of at least part of the 3D reconstruction, responsive to theassociated camera position and orientation within the at least part ofthe environment.
 8. The method according to claim 1, in which each ofone or more obtained video footage is one or more of: i. previouslyrecorded video footage; and ii. a live video stream.
 9. The methodaccording to claim 1 in which video footage for a plurality ofsimultaneous viewpoints is available, the method comprising the stepsof: obtaining a session ID associated with at least a first one of thevideos; and identifying and obtaining at least a second one other of thevideos using the session ID; and in which the step of rendering a viewcomprises switching from the first video to the second video; andrendering a view of the second video footage in alignment with acorresponding view of at least part of the 3D reconstruction, responsiveto the position and orientation of the first camera in the second videofootage within the at least part of the environment.
 10. The methodaccording to claim 1 in which the step of rendering a view comprises thestep of: rendering one or more representations of virtual dynamicobjects, the dynamic objects not being part of the 3D reconstruction andbeing located with respect to the second camera and the 3Dreconstruction behind the video image, the representations of virtualdynamic objects being displayed in front of the video image.
 11. Anon-transitory, computer readable medium having computer executableinstructions stored thereon, which when executed by a computer system,cause the computer system to perform a method of video playback,comprising: obtaining a 3D reconstruction of at least part of anenvironment; obtaining video footage of an activity within that at leastpart of the environment; obtaining data indicating a position andorientation of a first camera within the at least part of theenvironment that recorded the obtained video footage; and rendering aview of the video footage in alignment with a corresponding view of atleast part of the 3D reconstruction, responsive to the position andorientation of the first camera within the at least part of theenvironment, wherein: the 3D reconstruction of at least part of virtualenvironment is obtained from images, depth data and camera position datagenerated by at least one of: (i) a virtual camera that does notcorrespond to an in-game participant and is free to move in threedimensions, and (ii) one or more participants of a videogame, and theobtaining the 3D reconstruction of at least part of the environmentincludes: obtaining a first sequence of video images output from avideogame title; obtaining a corresponding sequence of in-game virtualcamera positions at which the video images were created; obtaining acorresponding sequence of depth buffer values for a depth buffer used bythe videogame whilst creating the video images; and for each of aplurality of video images and corresponding depth buffer values of theobtained sequences, obtaining mapping points corresponding to a samplingdistribution of points over the area of a respective video image andtheir associated depth values; wherein respective mapping points areobtained by projecting co-ordinates derived from the sample points fromthe video image and associated depth values back into a 3D game worldco-ordinate system of the videogame title, thereby obtaining a pointcloud dataset of mapping points corresponding to the first sequence ofvideo images.
 12. An entertainment device, comprising a receiveroperable to obtain a 3D reconstruction of at least part of anenvironment; a receiver operable to obtain video footage of an activitywithin that at least part of the environment; a receiver operable toobtain data indicating a position and orientation of a first camerawithin the at least part of the environment that recorded the obtainedvideo footage; and a rendering processor operable to render a view ofthe video footage in alignment with a corresponding view of at leastpart of the 3D reconstruction, responsive to the position andorientation of the first camera within the at least part of theenvironment, wherein: the 3D reconstruction of at least part of virtualenvironment is obtained from images, depth data and camera position datagenerated by at least one of: (i) a virtual camera that does notcorrespond to an in-game participant and is free to move in threedimensions, and (ii) one or more participants of a videogame, and theobtaining the 3D reconstruction of at least part of the environmentincludes: obtaining a first sequence of video images output from avideogame title; obtaining a corresponding sequence of in-game virtualcamera positions at which the video images were created; obtaining acorresponding sequence of depth buffer values for a depth buffer used bythe videogame whilst creating the video images; and for each of aplurality of video images and corresponding depth buffer values of theobtained sequences, obtaining mapping points corresponding to a samplingdistribution of points over the area of a respective video image andtheir associated depth values; wherein respective mapping points areobtained by projecting co-ordinates derived from the sample points fromthe video image and associated depth values back into a 3D game worldco-ordinate system of the videogame title, thereby obtaining a pointcloud dataset of mapping points corresponding to the first sequence ofvideo images.